A sum of money doubles itself in 10 years at simple interest. In how many years will it become three times?

A. 15
B. 20
C. 25
D. 30

Solution:
If money doubles in 10 years → 100% SI in 10 years → Rate = 10%
To become 3 times → 200% SI needed → 200 ÷ 10 = 20 years
Answer: B