A sum of money becomes four times in 8 years at simple interest. Find the rate of interest.
Correct: D
Let the principal amount be P and the rate of interest be R. We are given that the amount becomes four times in 8 years, which means the amount after 8 years is 4P. The simple interest is given by the formula I = PRT/100, where I is the interest. Since the amount after 8 years is 4P, the interest is 3P. Substituting these values in the formula, we get 3P = P * R * 8 / 100, which implies R = (3 * 100) / 8 = 37.5.