A sum of money earning compound interest annually doubles itself after

1.	A sum of money earning compound interest annually doubles itself after 4 years. What is the rate of interest ? (take 21/4 = 1.19)1. 14%2. 19%3. 18%4. 15%
Answer» Correct Answer - Option 2 : 19% Given data: Time period t = 4 years After the four years Amount = 2p Formulae used : Amount = p (1 + r/100 )^t Calculations: Let the principal be 'p' Rate percent be 'r' 2p = p (1 + r/100)⁴ ⇒ 2 = (1 + r/100)⁴ ⇒ 2^1/4 = 1 + r/100 ⇒ 2^1/4= (100 + r)/100 ⇒ 1.19 × 100 = 100 + r ⇒ 119 = 100 + r ⇒ r = 119 - 100 ⇒ r = 19 % ∴ The rate of interest is 19%

A sum of money earning compound interest annually doubles itself after 4 years. What is the rate of interest ? (take 21/4 = 1.19)1. 14%2. 19%3. 18%4. 15%

Answer» Correct Answer - Option 2 : 19%

Given data:

Time period t = 4 years

After the four years Amount = 2p

Formulae used :

Amount = p (1 + r/100 )^t

Calculations:

Let the principal be 'p'

Rate percent be 'r'

2p = p (1 + r/100)⁴

⇒ 2 = (1 + r/100)⁴

⇒ 2^1/4 = 1 + r/100

⇒ 2^1/4= (100 + r)/100

⇒ 1.19 × 100 = 100 + r

⇒ 119 = 100 + r

⇒ r = 119 - 100

⇒ r = 19 %

∴ The rate of interest is 19%

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A sum of money earning compound interest annually doubles itself after 4 years. What is the rate of interest ? (take 21/4 = 1.19)1. 14%2. 19%3. 18%4. 15%

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