Question

what is the rate of interest at which a sun of money would double itself in 25 years

Answer 1

Let the initial sum be P. Then, the final amount will be 2P, and hence, the Simple Interest for the duration of 2 years will be 2P - P = P. The formula for calculating SI is: SI = P x R x T / 100. Thus, according to the question at hand, SI = P, T = 2 years, and R is unknown.

P = P x R x 2 / 100

Or, R = 100/2 = 50

Thus, the rate of interest is 50% per annum.

The following infographic might help you in solving Aptitude type questions on Simple, as well as Compound, Interest