If a principal becomes twice of its amount in 10 years, the rate of simple interest per annum is (a) 5% (b) 10% (c) 15% (d) 20%

(b) 10 %

Explanation

Principal (P) = x

Amount (A) = 2x

Simple Interest (I) = 2x – x = x

Simple Interest (I) = \frac{\text{P × r × t}}{100}

or, x = \frac{\text{x × r ×10}}{100}

or, r = \frac{\text{x ×100}}{x × 10} = 10 %