An amount becomes double in 7 years on simple interest. The amount would be four times in ______ years on the same rate of simple interest.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 21.
A certain sum doubles in 7 years at simple interest, it means that
SI = 2P - P = P (Where P = Principal)
Similarly, If the amount becomes 4 times then SI = 3P
We know that If the rate is the same then,
Simple interest is proportional to time.
So,
7/T = P/3P
Where T= time taken to become 4 times the sum
T = 21 years