Question

 In 40 years an amount becomes 6 times the original amount. What is the rate of interest?​

Answer 1

SOLUTION

GIVEN

In 40 years an amount becomes 6 times the original amount.

TO DETERMINE

The rate of interest

EVALUATION

Let the original amount = Rs. P

Then by the given amount after 40 years

= Rs. 6P

Thus we have

Principal = P

Interest = I = 6P - P = 5P

Rate of interest = R%

Time = T years = 40 years

So by the given condition

$\displaystyle \sf{ I = \frac{PRT}{100} }$

$\displaystyle \sf{ \implies 5P = \frac{P \times R \times 40}{100} }$

$\displaystyle \sf{ \implies 5 = \frac{ R \times 40}{100} }$

$\displaystyle \sf{ \implies R = \frac{5 \times 100}{40} }$

$\displaystyle \sf{ \implies R = 12.5}$

FINAL ANSWER

Hence the required rate of interest = 12.5%

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