Question

10. How long will it take a given sum of money ( Say in Rupees ) to increase 4 times its present value when compounded half yearly at 7 % rate of interest ?(genuine answered please)​

Answer 1

Let the sum of money = P

Rate = 7% yearly. So, hslf-yearly rate = 7/2 = 3.5% = 0.035 in decimal

Let the time = t in years

P will become 4P

So, P * (1+0.035)^(2 * t) = 4P

Pr, ((1.035)^2)^t = 4P/P = 4

Or , (1.071225)^t = 4

Taking logarithm on both sides,

t log1.071225 = log4

Or, t = log4/log.071225 = 20.15 years I.e., 20 years and 0.15*12 = 1.8 or 2 months Ans.