Q140
ArithmeticSimple & Compound Interest
A certain sum of money at a certain rate of simple interest becomes double in 5 years. It will become four times in:
- a.$7\frac{1}{2}$ years
- b.10 years
- c.15 years
- d.20 years
Answer: (C) 15 years
Doubling in 5 years means interest of 100% in 5 years, i.e. 20% a year. Becoming four times needs 300% interest, which takes 15 years. 10 years would be right only for compound growth.