Question : A certain sum doubles in 7 years at Simple Interest. The same sum under the same interest will become 4 times in how many years?
Option 1: 14 years
Option 2: 28 years
Option 3: 21 years
Option 4: 10 years
Correct Answer: 21 years
Solution :
Let the sum be
Total amount for 7 years =
Simple Interest for 7 years =
If total amount =
Simple Interest =
Since in 7 years interest is
Hence, the correct answer is 21 years.