1.

A sum of money becomes eight times in 3 years, if the rate is compounded annually. In how much time will the same amount at the same compound rate become thirty-two times?1). 6 years2). 4 years3). 8 years4). 5 years

Answer»

⇒ Let, Principal be RS. x then Amount = Rs. 8x, Rate = r% and TIME (n) = 3 years.

⇒ A = P × [1+ (r/100)]n

⇒ 8x = x × [1 +(r/100)]3

⇒ 23 = [1+ (r/100)]3

⇒ 2 = 1 + (r/100) ------ 1

⇒ Amount becomes 16x then

⇒ A = P × [1+ (r/100)]n

32X = x × [1+ (r/100)]n

⇒ putting the value from equation 1 we get

32 = 2n

⇒ 25 = 2n

∴ n = 5


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