If a sum of money doubles itself on simple interest in 7 years, then in how many years will it become 4 times of itself ?
Answer & explanation
Correct answer: option 4
Let Principal = P , Amount = 2P , Time = 7 years and rate = R%
Amount = Principal + SI
SI = A - P
= 2P - P = P
SI = \(\frac{P × R × T}{100}\)
P = \(\frac{P × R × 7}{100}\)
R = \(\frac{100}{7}\)%
When amount got 4 times ,
A = 4P , Principal = P
SI = 3P
Now,
SI = \(\frac{P × R × T}{100}\)
3P = \(\frac{P × 100 × T}{100 × 7}\)
T = 21 years
The correct answer is option (4) : 21