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551.

If two positive integers a and b are written as a = x3 y2 and b = xy3, where x, y are prime numbers, then HCF (a,b) isA. xyB. xy2C. x3y3D. x2y2

Answer»

B. xy2

Let a = x3y2 = x × x × x × y × y

And b = xy3 = x × y × y × y

⇒ HCF of a and b = HCF (x3y2, xy3) = x × y × y = xy2

[Since, HCF is the product of the smallest power of each common prime factor involved in the numbers]

552.

An electronic device makes a beep after every 60 seconds. Another device makes a beep after every 62 seconds. They beeped together at 10 a.m. At what time will they beep together at the earliest?

Answer»

Beep duration of first device = 60 seconds 

Beep duration of second device = 62 seconds 

∴ Interval of beeping together = LCM (60, 62) 

Prime factorization: 

60 = 22 × 3 × 5 

62 = 2 × 31 

∴ LCM = 22 × 3 × 5 × 31 = 1860 seconds = 1860/60 = 31min 

Hence, they will beep together again at 10 : 31 a.m

553.

If p is a positive prime number then √p.(A) irrational number(B) rational number(C) integer number(D) none of these

Answer»

Answer is (A) irrational number

554.

An electronic device makes a beep after every 60 seconds. Another device makes a beep after every 62 seconds. They beeped together at 10 a.m. At what time will they beep together at the earliest?

Answer»

Given:

Beep duration of first device = 60 seconds

Beep duration of second device = 62 seconds

To find the interval of beeping together, we need to find the LCM of 60 and 62 first.

60 = 2 x 2 × 3 × 5

62 = 2 × 31

LCM = 2 x 2 × 3 × 5 × 31 = 1860 seconds

Convert time into mins:

160 sec = 1860/60 mins = 31 min

Electronic devices will beep after every 31 minutes.

Hence, both devices will beep together again at 10:31 a.m. again.

555.

If p/q (q ≠ 0) is a rational  number then what condition apply for q whereas p/q is a terminating decimal ? Is a rational number is terminating decimal.

Answer»

p/q (q ≠ 0) is a rational number.

and p/q is terminating decimal.

Prime factor of q will be in the form 2m x 5n 

where m, n is non-negative integers.

556.

In the decimal expansion of rational  number 43/(22 x 53), after how many digits decimal will end?(a) 1(b) 2(c) 3(d) 4

Answer»

Answer is (c) 3

43/(22 x 53)

Multiply by 2 in numerator and denominator of number

43/(22 x 53) = 86/103 = 0.086

557.

Prove that (2 √3 – 1) is irrational.

Answer»

Let x = 2 √3 – 1 be a rational number. 

x = 2 √3 – 1 

⇒ x2 = (2 √3 – 1)2 

⇒ x2 = (2 √3 )2 + (1)2 – 2(2 √3)(1) 

⇒ x2 = 12 + 1 - 4 √3

⇒ x2 – 13 = - 4 √3

⇒ \(\frac{13-x^2}4\) = √3

Since x is rational number, x2 is also a rational number. 

⇒ 13 - x2 is a rational number

⇒ \(\frac{13-x^2}4\) is a rational number

⇒ √3 is a rational number 

But √3 is an irrational number, which is a contradiction. 

Hence, our assumption is wrong. 

Thus, (2 √3 – 1) is an irrational number.

558.

Prove that \(\frac{1}{\sqrt3}\) is irrational.

Answer»

Let \(\frac{1}{\sqrt3}\) be rational.

∴ \(\frac{1}{\sqrt3}\) = \(\frac{a}{b}\), where a, b are positive integers having no common factor other than 1

∴ \(\sqrt3\) = \(\frac{b}{a}\).....(1)

Since a, b are non-zero integers, \(\frac{b}{a}\) is rational.

Thus, equation (1) shows that \(\sqrt3\) is rational.

This contradicts the fact that \(\sqrt3\) is rational.

The contradiction arises by assuming \(\sqrt3\) is rational.

Hence, \(\frac{1}{\sqrt3}\) is irrational.

559.

State whether the given statement is true or false.(i) The sum of two rationals is always rational.(ii) The product of two rationals is always rational.(iii) The sum of two irrationals is always an irrational.(iv) The product of two irrationals is always an irrational.(v) The sum of a rational and an irrational is irrational.(vi) The product of a rational and an irrational is irrational.

Answer»

(i) True.

(ii) True.

(iii) False.

Reason:

Sum of two irrational can be rational. Let us take an example,

Consider two irrational numbers: (3 + √2) and (3 – √2)

Sum: (3 + √2) + (3 – √2) = 3 + √2 + 3 – √2 = 6 which is rational.

(iv) False.

Reason:

Product of two irrational numbers can be rational. Let us take an example,

Consider two irrational numbers: (3 + √2) and (3 – √2)

Product: (3 + √2)(3 – √2 ) 

= (3)2 – (√2 )2 

= 9 – 2 = 7; which is rational

(v) True.

(vi) True.

560.

State whether the given statement is true or false: (i) The sum of two rationals is always rational (ii) The product of two rationals is always rational (iii) The sum of two irrationals is an irrational (iv) The product of two irrationals is an irrational (v) The sum of a rational and an irrational is irrational (vi) The product of a rational and an irrational is irrational

Answer»

(i) The sum of two rationals is always rational - True 

(ii) The product of two rationals is always rational - True 

(iii) The sum of two irrationals is an irrational - False 

Counter example: 2 + √3 and 2 - √3 are two irrational numbers. But their sum is 4, which is a rational number. 

(iv) The product of two irrationals is an irrational – False 

Counter example: 

2 √3 and 4 √3 are two irrational numbers. But their product is 24, which is a rational number. 

(v) The sum of a rational and an irrational is irrational - True 

(vi) The product of a rational and an irrational is irrational - True

561.

State whether the given statement is true or false: (i) The sum of two rationals is always rational (ii) The product of two rationals is always rational (iii) The sum of two irrationals is an irrational (iv) The product of two irrationals is an irrational (v) The sum of a rational and an irrational is irrational (vi) The product of a rational and an irrational is irrational

Answer»

(i) The sum of two rationals is always rational - True 

(ii) The product of two rationals is always rational - True 

(iii) The sum of two irrationals is an irrational - False Counter example: 2 + √3 and 2 - √3 are two irrational numbers. But their sum is 4, which is a rational number. 

(iv) The product of two irrationals is an irrational – False Counter example: 2 √3 and 4 √3 are two irrational numbers. But their product is 24, which is a rational number. 

(v) The sum of a rational and an irrational is irrational - True 

(vi) The product of a rational and an irrational is irrational - True

562.

Decimal expansion of which of the following is non-terminating recurring?  (A)  2/5  (B) 3/16  (C) 3/11 (D) 137/25

Answer»

Correct option is (C) \(\frac3{11}\)

563.

Which of the following has a terminating decimal expansion?(a) \(\frac{32}{91}\) (b) \(\frac{19}{80}\)(c) \(\frac{23}{45}\)(d) \(\frac{25}{42}\)

Answer»

(b) \(\frac{19}{80}\)

\(\frac{19}{80}\) = \(\frac{19}{2^4\times5}\)

We know 2 and 5 are not factors of 19, so it is in its simplest form. 

And (24 × 5) = (2m × 5n

Hence, \(\frac{19}{80}\) is a terminating decimal.

564.

A sweet seller has 420 Kaju burfies and 130 Badam burfies. She wants to stock them in such a way that each stock has the same number and they take up the least area of the tray. What is the number of burfies that can be placed in each stock for this purpose ? (A) 15 (B) 10 (C) 40 (D) 45

Answer»

Correct option is (B) 10

Required number is HCF of 420 and 130.

\(\therefore\) Required number = HCF (420, 130)

= 10

Correct option is (B) 10

565.

Without actually performing the long division, state whether the following rational numbers will have a terminating decimal expansion or a non-terminating repeating decimal expansion.(i) \(\frac{23}{8}\)(ii) \(\frac{125}{441}\)(iii) \(\frac{35}{50}\)(iv) \(\frac{77}{210}\)(v) \(\frac{129}{(2^2 \times 5^7 \times 7^{17})}\)(vi) \(\frac{987}{10500}\)

Answer»

(i) \(\frac{23}{8}\)

We have, \(\frac{23}{8}\) and here the denominator is 8. 

⇒ 8 = 23 x 5 

We see that the denominator 8 of \(\frac{23}{8}\) is of the form 2m x 5n, where m, n are non-negative integers. 

Hence, \(\frac{23}{8}\) has terminating decimal expansion. And, the decimal expansion of \(\frac{23}{8}\) terminates after three places of decimal.

(ii) \(\frac{125}{441}\)

We have, \(\frac{125}{441}\) and here the denominator is 441. 

⇒ 441 = 32 x 72 

We see that the denominator 441 of \(\frac{125}{441}\) is not of the form 2m x 5n, where m, n are non-negative integers. 

Hence, \(\frac{125}{441}\) has non-terminating repeating decimal expansion.

(iii) \(\frac{35}{50}\)

We have, \(\frac{35}{50}\) and here the denominator is 50. 

⇒ 50 = 2 x 52 

We see that the denominator 50 of \(\frac{35}{50}\) is of the form 2m x 5n, where m, n are non-negative integers. 

Hence, \(\frac{35}{50}\) has terminating decimal expansion. And, the decimal expansion of \(\frac{35}{50}\) terminates after two places of decimal.

(iv) \(\frac{77}{210}\)

We have, \(\frac{77}{210}\) and here the denominator is 210. 

⇒ 210 = 2 x 3 x 5 x 7 

We see that the denominator 210 of \(\frac{77}{210}\) is not of the form 2m x 5n, where m, n are non-negative integers. 

Hence, \(\frac{77}{210}\) has non-terminating repeating decimal expansion.

(v) \(\frac{129}{(2^2 \times 5^7 \times 7^{17})}\)

We have, \(\frac{129}{(2^2 \times 5^7 \times 7^{17})}\) and here the denominator is 22 x 57 x 717

Clearly, 

We see that the denominator is not of the form 2m x 5n, where m, n are non-negative integers. 

And hence, \(\frac{129}{(2^2 \times 5^7 \times 7^{17})}\) has non-terminating repeating decimal expansion.

(vi) \(\frac{987}{10500}\)

We have, \(\frac{987}{10500}\) 

But, \(\frac{987}{10500}\) = \(\frac{47}{500}\) (reduced form) 

And now the denominator is 500. 

⇒ 500 = 22 x 53 

We see that the denominator 500 of \(\frac{47}{500}\) is of the form 2m x 5n, where m, n are non-negative integers. 

Hence, \(\frac{987}{10500}\) has terminating decimal expansion. And, the decimal expansion of \(\frac{987}{10500}\) terminates after three places of decimal.

566.

Without actually performing the long division, state whether 13/3125 has terminating decimal expansion or not.

Answer»

13/3125=13/20x 55

This, shows that the prime factorisation of the denominator is of the form 2m × 5n.

Hence, it has terminating decimal expansion.

567.

Check whether 6n can end with the digit ‘0’ for any natural number n.

Answer»

Given number = 6n = (2 × 3)n 

The prime factors here are 2 and 3 only. 

To be end with 0; 6n should have a prime factor 5 and also 2. So, 6n can’t end with zero.

568.

There is a circular path around a sports field. Priya takes 18 minutes to drive one round of the field, while Ravish takes 12 minutes for the same. Suppose they both start at the same point and at the same time, and go in the same direction.(i) After how many minutes will they meet again at the starting point ?(ii) Which mathematical concept is used in this problem?(iii) What value is discussed in this problem ?

Answer»

(i) Required number of minutes is the LCM of 18 and 12.

18 = 2 x 32

and 12 =  22 x 3 

.'. LCM of 18 and 12 = 22 x 32 = 36

Hence, Ravish and Priya will meet again at the starting point after 36 minutes.

(ii) LCM of numbers

(iii) Healthy competition is necessary for personal development and progress

569.

There is a circular path around a sports field. Anand takes 18 minutes to drive one round of the field while Prakash takes 12 minutes for the same. Suppose they both start at the same point and at the same time and go in the same direction. After how many minutes will they meet again at the starting point ? (A) 36 minutes (B) 19 minutes (C) 48 minutes (D) 56 minutes

Answer»

Correct option is (A) 36 minutes

570.

The decimal expansion of 9/17 is ………………(A) Terminating(B) Non-terminating and non-repeating (C) Non-terminating and repeating (D) Terminating and repeating

Answer»

Correct option is (C) Non-terminating and repeating

\(\frac{9}{17};\) denominator = 17

\(\therefore\) Prime factors of denominator is other than 2 or 5.

\(\therefore\) \(\frac{9}{17}\) has non-terminating and repeating decimals.

Correct option is (C) Non-terminating and repeating

571.

There is a circular path around a sports field. Preeti takes 18 minutes to drive one round of the field, while Suman takes 12 minutes for the same. Suppose they both start at the same point and at the same time, and go in the same direction. After how many minutes will they meet again at the starting point?

Answer»

Solution:

They will be meet again after LCM of both values at the starting point.
To get the LCM we have to factorize the number.
18        = 2 × 3 × 3
12        = 2 × 2 × 3
LCM    = 2 × 2 × 3 × 3 = 36 
Therefore, they will meet together at the starting point after 36 minutes.

572.

Show that any number of the form 4n , n ϵ N can never end with the digit 0.

Answer»

If 4n ends with 0, then it must have 5 as a factor. 

But we know the only prime factor of 4n is 2. 

Also we know from the fundamental theorem of arithmetic that prime factorization of each number is unique. 

Hence, 4n can never end with the digit 0.

573.

Examine whether 17/30 is a terminating decimal.

Answer»

17/30 = 17/ (2 × 3 × 5) 

We know that 2,3 and 5 are not the factors of 17. 

So, 17/30 is in its simplest form. 

Also, 30 = 2 × 3 × 5 ≠ (2m × 5n

Hence, 17/30 is a non-terminating decimal.

574.

The HCF of two numbers is 27 and their LCM is 162. If one of the numbers is 54, what is the other number? (a) 36 (b) 45 (c) 9 (d) 81

Answer»

(d) 81 

Let the two numbers be x and y. 

It is given that: x = 54 

HCF = 27 

LCM = 162 

We know, 

x × y = HCF × LCM 

⇒ 54 × y = 27 × 162 

⇒ 54 y = 4374 

⇒ ∴ y = 4374/54 

= 81

575.

The HCF of two numbers is 27 and their LCM is 162. If one of the numbers is 54, what is the other number? (a) 36 (b) 45 (c) 9 (d) 81

Answer»

(d) 81 

Let the two numbers be x and y. 

It is given that: 

x = 54 

HCF = 27 

LCM = 162 

We know, 

x × y = HCF × LCM 

⇒ 54 × y = 27 × 162 

⇒ 54 y = 4374

⇒ ∴ y = \(\frac{4374}{54}\) = 81

LCM * HCF = Number 1 * Number 2

27 * 162 = 54 * x

x = 81.
576.

The HCF of two numbers is 18 and their product is 12960. Find their LCM

Answer»

HCF of two numbers = 18 

Product of two numbers = 12960 

Let their LCM be x. 

Using the formula, product of two numbers = HCF × LCM 

we conclude that 

12960 = 18 × x 

x = 12960/18 = 720 

Hence, their LCM is 720.

577.

The HCF of two numbers is 27 and their LCM is 162. If one of the number is 81, find the other

Answer»

Let the two numbers be x and y 

It is given that: 

x = 81 

HCF = 27 and LCM = 162 

We know, Product of two numbers = HCF × LCM 

⇒ x × y = 27 × 162 

⇒ 81 × y = 4374 

⇒ y = 4374/81 = 54 

Hence, the other number is y is 54.

578.

The HCF of two numbers is 23 and their LCM is 1449. If one of the numbers is 161, find the other

Answer»

Let the two numbers be a and b. 

Let the value of a be 161. 

Given: HCF = 23 and LCM = 1449 

We know, a × b = HCF × LCM 

⇒ 161 × b = 23 × 1449 

⇒ ∴ b = 23 ×1449/ 161 = 33327/161 = 207 

Hence, the other number b is 207.

579.

Prove that square of any positive integer of the form 5q + 1 is of the same form.

Answer»

Here, the integer ‘n’ is of the form 5q+1.

⇒ n= 5q+1 

On squaring it, 

⇒ n2= (5q+1)2 

⇒ n2= (25q2+10q+1) 

⇒ n2= 5(5q2+2q)+1 

⇒ n2= 5m+1, where m is some integer. [For m = 5q2+2q] 

Therefore, the square of any positive integer of the form 5q + 1 is of the same form.

580.

Prove that the square of any positive integer of the form 5q + 1 is of the same form.

Answer»

Let n = 5q + 1 where q is a positive integer
∴ n2 = (5q + 1)2
= 25q2 + 10q + 1
= 5(5q2 + 2q) + 1
= 5m + 1, where m is some integer
Hence, the square of any positive integer of the form 5q + 1 is of the same form.

581.

Show that the square of odd integer is of the form 8q + 1, for some integer q.

Answer»

From Euclid’s division lemma, 

a = bq+r ; where 0 < r < b 

Putting b=4 for the question, 

⇒ a = 4q + r, 0 < r < 4 

For r = 0, we get a = 4q, which is an even number. 

For r = 1, we get a = 4q + 1, which is an odd number. 

On squaring, 

⇒ a2 = (4q + 1)2 

= 16q2 + 1 + 8q 

= 8(2q2 + q) + 1 

= 8m + 1, where m = 2q2 + q 

For r = 2, we get a = 4q + 2 = 2(2q + 1), which is an even number. 

For r = 3, we get a = 4q + 3, which is an odd number. 

On squaring, 

⇒ a2 = (4q + 3)2 

= 16q2 + 9 + 24q 

= 8(2q2 + 3q + 1) + 1

= 8m + 1, where m = 2q2 + 3q + 1 

Thus, the square of an odd integer is of the form 8q + 1, for some integer q.

582.

Prove that the square of any positive integer is of the form 3m or 3m + 1 but not of the form 3m + 2.

Answer»

Let any positive integer ‘n’ be of the form 3q or, 3q+1 or 3q+2. (From Euclid’s division lemma for b= 3) 

If n= 3q, 

Then, on squaring 

⇒ n2= (3q)2 = 9q2 

⇒ n2= 3(3q2

⇒ n2= 3m, where m is some integer [m = 3q2] 

If n= 3q+1, 

Then, on squaring 

⇒ n2= (3q+1)2 = 9q2 + 6q + 1 

⇒ n2= 3(3q2 +2q) + 1 

⇒ n2= 3m + 1, where m is some integer [m = 3q2 +2q] 

If n= 3q+2, 

Then, on squaring 

⇒ n2= (3q+2)2 = 9q2 + 12q + 4 

⇒ n2= 3(3q2 + 4q + 1) + 1 

⇒ n2= 3m, where m is some integer [m = 3q2 + 4q + 1] 

Thus, it is observed that the square of any positive integer is of the form 3m or 3m + 1 but not of the form 3m + 2.

583.

Prove that the square of any positive integer is of the form 5q or 5q + 1, 5q + 4 for some integer q.

Answer»

Let ‘a’ be any positive integer. 

Then,

According to Euclid’s division lemma, 

a = bq+r 

According to the question, when b = 5. 

a = 5k + r, 0 < r < 5 

When r = 0, we get, a = 5k 

a2 = 25k2 = 5(5k2) = 5q, where q = 5k2 

When r = 1, we get, a = 5k + 1 

a2 = (5k + 1)2 

= 25k2 + 1 + 10k 

= 5k(5k + 2) + 1 

= 5q + 1, where q = k(5k + 2) 

When r = 2, we get, a = 5k + 2 

a2 = (5k + 2)2 

= 25k2 + 4 + 20k 

= 5(5k2 + 4k) + 4 

= 4q + 4, where q = 5k2 + 4k 

When r = 3, we get, a = 5k + 3 

a2 = (5k + 3)

= 25k2 + 9 + 30k 

= 5(5k2 + 6k + 1) + 4 

= 5q + 4, where q = 5k2 + 6k + 1 

When r = 4, we get, a = 5k + 4 

a2 = (5k + 4)2 

= 25k2 + 16 + 40k 

= 5(5k2 + 8k + 3) + 1 

= 5q + 1, where q = 5k2 + 8k + 3 

Therefore, the square of any positive integer is of the form 5q or, 5q + 1 or 5q + 4 for some integer q.

584.

Prove that the square of any positive integer is of the form 4q or 4q + 1 for some integer q.

Answer»

By Euclid’s division Algorithm
a = bm + r, where 0 ≤ r ≤ b
Put b = 4
a = 4m + r, where 0 ≤ r ≤ 4
If r = 0, then a = 4m
If r = 1, then a = 4m + 1
If r = 2, then a = 4m + 2
If r = 3, then a = 4m + 3
Now, (4m)2 = 16m2
= 4 × 4m2
= 4q where q is some integer
(4m + 1)2 = (4m)2 + 2(4m)(1) + (1)2
= 16m2 + 8m + 1
= 4(4m2 + 2m) + 1
= 4q + 1 where q is some integer
(4m + 2)2 = (4m)2 + 2(4m)(2)+(2)2
= 16m2 + 24m + 9
= 16m2 + 24m + 8 + 1
= 4(4m2 + 6m + 2) + 1
= 4q + 1, where q is some integer

Hence, the square of any positive integer is of the form 4q or 4q + 1 for some integer m​

585.

Prove that the square of any positive integer is of the form 4q or 4q + 1 for some integer q.

Answer»

Since any positive integer n is of the form 2p or, 2p + 1

When n = 2p,

then n2 = 4p2 = 4a

where a = p2

When n = 2p + 1,

then n2 = (2p + 1)2 = 4p2 + 4p + 1

⇒ 4p(p + 1) + 1 ⇒ 4m + 1

where m = p(p + 1)

Therefore square of any positive integer is of the form 4q or 4q + 1 for some integer q

586.

Using Euclid’s division algorithm, find which of the following pairs of numbers are co-prime: (i) 231, 396 (ii) 847, 2160

Answer»

Let us find the HCF of each pair of numbers. 

(i) 396 = 231 × 1 + 165 

231 = 165 × 1 + 66 

165 = 66 × 2 + 33 

66 = 33 × 2 + 0 

Therefore, HCF = 33. Hence, numbers are not co-prime

(ii) 2160 = 847 × 2 + 466 

847 = 466 × 1 + 381 

466 = 381 × 1 + 85 

381 = 85 × 4 + 41 

85 = 41 × 2 + 3 

41 = 3 × 13 + 2 

3 = 2 × 1 + 1 

2 = 1 × 2 + 0 

Therefore, the HCF = 1. Hence, the numbers are co-prime.

587.

Show that the square of any positive integer is either of the form 4q or 4q + 1 for some integer q.

Answer»

According to Euclid’s division lemma,

a=bq+r

According to the question,

When b = 4.

a = 4k + r, 0 < r < 4

When r = 0, we get, a = 4k

a2 = 16k2 = 4(4k2) = 4q, where q = 4k2

When r = 1, we get, a = 4k + 1

a2 = (4k + 1)2 = 16k2 + 1 + 8k = 4(4k + 2) + 1 = 4q + 1, where q = k(4k + 2)

When r = 2, we get, a = 4k + 2

a2 = (4k + 2)2 = 16k2 + 4 + 16k = 4(4k2 + 4k + 1) = 4q, where q = 4k2 + 4k + 1

When r = 3, we get, a = 4k + 3

a2 = (4k + 3)2 = 16k2 + 9 + 24k = 4(4k2 + 6k + 2) + 1

= 4q + 1, where q = 4k2 + 6k + 2

Therefore, the square of any positive integer is either of the form 4q or 4q + 1 for some integer q.

Hence Proved.

588.

The collection of negative numbers and whole numbers is denoted by A) Q B) W C) Z or lD) N

Answer»

Correct option is (C) Z or l

Z or I = {...., -3, -2, -1, 0, 1, 2, 3, .....}

Correct option is  C) Z or l

589.

Show that the square of an odd positive integer is of the form 8m + 1, for some whole number m.

Answer»

Any positive odd integer is of the form 2q + 1, where q is a whole number. 

Therefore, (2q + 1)2 = 4q2 + 4q + 1 = 4q (q + 1) + 1, ...... (1) 

q (q + 1) is either 0 or even. So, it is 2m, where m is a whole number. 

Therefore, (2q + 1)2 = 4.2 m + 1 = 8 m + 1. [From (1)]

590.

If p3 + q3 = r3 then logp (r – q) + logp (r2 + qr + q2 ) ……………….. (A) 3 (B) 8 (C) 9 (D) 14

Answer»

Correct option is (A) 3

Given that \(p^3+q^3=r^3\)

\(\Rightarrow\) \(p^3=r^3-q^3\) \(=(r-q)(r^2+qr+q^2)\)

\(\Rightarrow\) \(log_p\,p^3\) \(=log_p((r-q)(r^2+qr+q^2))\)   (By taking \(log_p\) both sides)

\(\Rightarrow\) \(log_p(r-q)+log_p(r^2+qr+q^2)\) \(=3\,log_p\,p=3\)

Correct option is (A) 3

591.

\(^3\sqrt{a}\) + \(^3\sqrt{b}\) + \(^3\sqrt{c}\) = 0 then (a + b + c)3 =................(A) 3 abc (B) 9 abc (C) 27 abc (D) 81 abc

Answer»

Correct option is (C) 27 abc

We have \(\sqrt[3]a+\sqrt[3]b+ \sqrt[3]c=0\)

\(\Rightarrow\) \(a^\frac13+b^\frac13+c^\frac13=0\)

\(\Rightarrow\) \(a^\frac13+b^\frac13=-c^\frac13\)    ___________(1)

\(\Rightarrow\) \((a^\frac13+b^\frac13)^3=(-c^\frac13)^3\)  (By cubing both sides)

\(\Rightarrow(a^\frac13)^3+(b^\frac13)^3+3a^\frac13b^\frac13(a^\frac13+b^\frac13)=-(c^\frac13)^3\)  \((\because(a+b)^3=a^3+b^3+3ab(a+b)\,\&\,(ab)^3=a^3b^3)\)

\(\Rightarrow a+b+3\,a^\frac13\,b^\frac13\times-c^\frac13=-c\)   (From (1))

\(\Rightarrow\) a+b+c \(=3\,a^\frac13\,b^\frac13c^\frac13\)

\(\Rightarrow\) \((a+b+c)^3\) \(=(3\,a^\frac13\,b^\frac13c^\frac13)^3\)   (By cubing both sides)

\(\Rightarrow\) \((a+b+c)^3=27\,abc\)    \((\because(ab)^m=a^mb^m)\)

Correct option is (C) 27 abc

592.

The product of first 2019 whole numbers……A) 0 B) 2019 C) 1.2.3.4 …………..2018.2019 D) 1 + 2 + 3 + ………………+ 2019

Answer»

Correct option is (A) 0

\(\because\) First whole number is zero.

\(\therefore\) Product of first 2019 whole numbers is zero.

\((\because\) 0 . 1 . 2 . 3 . 4 ....... 2019 = 0)

Correct option is  A) 0

593.

If \(\cfrac{\sqrt7-\sqrt{3}}x\) = \(\cfrac{x}{\sqrt{7}+\sqrt{3}}\) then the value of x = ……………A) 11 B) 2 C) 16 D) 12

Answer»

Correct option is (B) 2

\(x^2=({\sqrt7-\sqrt3})({\sqrt7+\sqrt3})\)

= 7 - 3 = 4 = \(2^2\)

\(\Rightarrow\) x = 2

Correct option is B) 2

594.

The LCM of the numbers 27 x 34 x 7 and 23 x 34 x 11 isA) 23 × 34 B) 27 × 34C) 27 × 34 × 7 × 11 D) 23 × 34 × 7 × 11

Answer»

Correct option is (C) 27 × 34 × 7 × 11

LCM of the numbers \(2^7\times3^4\times7\) and \(2^3\times3^4\times11\) is  \(2^7\times3^4\times7\times11.\)

Correct option is C) 27 × 34 × 7 × 11 

595.

Express 3.25 in the form of p/q.A) \(\frac{13}{4}\)B) \(\frac{65}{2}\)C) \(\frac{13}{40}\)D) \(\frac{13}{20}\)

Answer»

Correct option is (A) \(\frac{13}{4}\)

\(3.25=\frac{325}{100}\)

\(=\frac{325\div25}{100\div25}=\frac{13}{4}\)

Correct option is  \(\frac{13}{4}\)

596.

(-2/3)2/7 x (-2/3)5/7 = ...................A)1 B) -2/3C) 0 D) (-2/3)2/5

Answer»

Correct option is (B) -2/3

\((\frac{-2}{3})^\frac27\times(\frac{-2}{3})^\frac57\) \(=(\frac{-2}{3})^{\frac27+\frac57}\)

\(=(\frac{-2}{3})^1=\frac{-2}{3}\)

Correct option is  B) -2/3

597.

A rational number equivalent to -3/4 isA) -4/3B) -4/5C) 3/4D) -6/8

Answer»

Correct option is (D) -6/8

\(\frac{-6}{8}=\frac{-6\div2}{8\div2}\) \(=\frac{-3}{4}\)

Hence, \(\frac{-6}{8}\) is equivalent to rational number \(\frac{-3}{4}.\)

Correct option is  D) -6/8

598.

Rationalising factor of \(^3\sqrt{16}\) - \(^3\sqrt{4}\) + 1 is ………………(A) \(^3\sqrt{4}\) + 2 (B) \(^3\sqrt{4}\) – 2 (C) \(^3\sqrt{4}\) + 1 (D) \(^3\sqrt{4}\) – 1

Answer»

Correct option is (C) \(\sqrt[3]4+1\)

A rationalising factor of a given irrational number is an irrational number whose multiple with given irrational number gives a rational number.

(A) \((16^\frac13-4^\frac13+1)(4^\frac13+2)\)

\(=64^\frac13-16^\frac13+4^\frac13+2.16^\frac13-2.4^\frac13+2\)

\(=(4^3)^\frac13+16^\frac13-4^\frac13+2\)

\(=4+2+16^\frac13-4^\frac13\)

\(=6+16^\frac13-4^\frac13\) which is an irrational number.

Thus, \((4^\frac13+2)\) is not a rationalising factor of \((16^\frac13-4^\frac13+1).\)

(B) \((16^\frac13-4^\frac13+1)(4^\frac13-2)\)

\(=64^\frac13-16^\frac13+4^\frac13-2.16^\frac13+2.4^\frac13-2\)

\(=(4^3)^\frac13-3.16^\frac13+3.4^\frac13-2\)

\(=4-2-3.16^\frac13+3.4^\frac13\)

\(=2-3.16^\frac13+3.4^\frac13\) which is an irrational number.

Thus, \((4^\frac13-2)\) is not a rationalising factor of \((16^\frac13-4^\frac13+1).\)

(C) \((16^\frac13-4^\frac13+1)(4^\frac13+1)\)

\(=64^\frac13-16^\frac13+4^\frac13+16^\frac13-4^\frac13+1\)

\(=(4^3)^\frac13+1\)

= 4+1 = 5 which is a rational number.

Thus, \((4^\frac13+1)\) is a rationalising factor of \((16^\frac13-4^\frac13+1).\)

(D) \((16^\frac13-4^\frac13+1)(4^\frac13-1)\)

\(=64^\frac13-16^\frac13+4^\frac13-16^\frac13+4^\frac13-1\)

\(=(4^3)^\frac13-2.16^\frac13+2.4^\frac13-1\)

\(=4-1-2.16^\frac13+2.4^\frac13\)

\(=3-2.16^\frac13+2.4^\frac13\) which is an irrational number.

Thus, \((4^\frac13-1)\) is not a rationalising factor of \((16^\frac13-4^\frac13+1).\)

Correct option is (C) \(^3\sqrt{4}\) + 1 

599.

A rationalising factor of \(^3\sqrt{25}\) + \(\cfrac{1}{^3\sqrt{25}}\) - 1 is ...................(A) 51/3 - 51/3(B) 51/3 + 51/3(C) 251/3 + 25-1/3(D) 251/3 - 25-1/3

Answer»

Correct option is (B) 51/3 + 51/3

\(\because\left((25)^\frac13+\frac1{(25)^\frac13}-1\right)\left(5^\frac13+\frac1{5^\frac13}\right)\)

\(=\left(5^\frac23+\frac1{5^\frac23}-1\right)\left(5^\frac13+\frac1{5^\frac13}\right)\)

\(=5^\frac23.5^\frac13+\cfrac{5^\frac13}{5^\frac23}-5^\frac13+\cfrac{5^\frac23}{5^\frac13}+\frac1{5^\frac23\,5^\frac13}-\frac1{5^\frac13}\)

\(=5^\frac33+\frac1{5^\frac13}-5^\frac13+5^\frac13+\frac1{5^\frac33}-\frac1{5^\frac13}\)   \((\because a^m.a^n=a^{m+n}\,and\,\cfrac{a^m}{a^n}=a^{m-n})\)

\(=5+\frac15=\frac{26}5\) which is a rational number.

Thus, \((5^{\frac{1}{3}}+\frac1{5^{\frac{1}{3}}})\) is a rationalising factor of \((25^\frac13+\frac1{25^\frac13}-1).\)

Correct option is (B) 51/3 + 51/3

600.

Radical form of \(3^\frac{1}{5}\) is A) \(\sqrt[5]{3^1}\) B) \(\sqrt[3]{5^1}\)C) \(\sqrt[5]{1^3}\)D) \(\sqrt[3]{1^5}\)

Answer»

Correct option is (A) \(\sqrt[5]{3^1}\)

\(3^\frac{1}{5}=\sqrt[5]{3}\)

\(\sqrt[5]{3^1}\)

Correct option is  A) \(\sqrt[5]{3^1}\)