A sum of money doubles itself in 8 years. What is the rate of interest?

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12.5

answer is C.

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Detailed Solution

Concept- There is a certain amount of money which has doubled after 8 years . and now we need to find the rate of interest from which it doubled by 8 years.
By using the formula of simple interest that is

According to the given question we have
Time =

years
So let assume that the money is

And money after 8 years is

So the difference between money after 8 years and the money at the time of investment will be our interest. That is

2 x - x = x

Hence, x is the interest.
Now let assume the rate of interest will be r .
By using the formula of simple interest we will get ,

SI = \frac{PRT}{100}

P is the principal amount that is x .
R is the rate of interest which we need to find assumed as r
T is the time that is 8 years.
So let’s put the value , we will get

SI = \frac{x \times 100}{x \times 8} = \frac{100}{8} = \frac{25}{2} = 12.5 %

So , the rate of interest will be 12.5 % per annum . Hence, the correct answer is 3) 12.5%

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