# At simple interest, a sum of money doubles itself in ten years. Find the number of years it will take to triple itself.

A. 20 years B. 24 years C. 25 years D. 30 years Answer: Option A
Let the principal be P. As per the question, Amount = 2(Principal) = 2P SI = Amount – Principal = 2P – P = P By formula, $\begin{array}{l}R=\frac{\text{SI}\times100}{P\times T}\\ R=\frac{P\times100}{P\times10}\\ =10\%\end{array}$ So, the rate is 10% per annum. Now, the sum gets tripled. A = 3(Principal) = 3P SI = 3P – P = 2P \begin{aligned} T &=\frac{S I \times 100}{P \times R} \\ T &=\frac{2 P \times 100}{P \times 10} \end{aligned} = 20 years