A sum of money at simple interest doubles in 7 years. It will be come four times in
A sum of money at simple interest doubles in 7 years. It will be come four times in
A90 years
B18 years
C38 years
D21 years
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Answer is : 21 years
Explanation:
let amount be x.
Case 1 : amount becomes 2x => simple interest = x
Case 2 : amount becomes 4x => simple interest = 3x
\(SI= \frac{P \times R \times T}{100}\)
i.e., SI ∝ T (when Rate of interest is constant)
x ∝ 7
3x ∝ n
\(\frac{x}{3x} = \frac{7}{n}\)\(=> \frac{1}{3}=\frac{7}{n}\)
\(=> n = 7 \times 3\)
n = 21 years
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