Question

In how many years a sum doubles itself at 4% rate of interest?​

Answer 1

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Let us assume that the initial sum is 's'. Now we are required to find the time, in which we get the interest as 's' such that amount equals twice the sum, which is '2s'.

It is given that the rate of interest is 4%.

According to Simple Interest Formula,

$\implies S.I. = \dfrac{P \times R \times t}{100}$

where, P is the principal (initial sum), R is the rate of interest and t is the time period.

Substituting the known values we get:

$\implies s = \dfrac{ s \times 4 \times t}{100}\\\\\\\implies 100.s = 4.s.t\\\\\\\implies t = \dfrac{100\times s}{4\times s}\\\\\\\implies \boxed{ \bf{ t = 25\:\:years}}$

Hence after 25 years, a sum will double itself at 4% rate of interest.