Question 75

A sum of money amounts to 5 times of itself in 20 years when invested at a certain rate of simple interest per annum. What is the rate of simple interest per annum that is on offer?

Solution

Let's assume the principal amount, rate of interest and time are P, R and T respectively.

A sum of money amounts to 5 times of itself in 20 years when invested at a certain rate of simple interest per annum.

interest = 5P-P = 4P

$$interest\ =\ \frac{P\times R\times T}{100}$$

$$4P\ =\ \frac{P\times R\times20}{100}$$

$$4\ =\ \frac{R}{5}$$
Rate of simple interest per annum = R = 20%

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