If a certain sum becomes 2 times in 7 years at compound interest then in how many years it will beco...........

Quantitative Aptitude (CPO) Compound Interest

If a certain sum becomes 2 times in 7 years at compound interest, then in how many years, it will become 8 times?

- If a sum doubles in 7 years at compound interest:

- The doubling formula: \(A = P \times (1 + r)^t\)

- Here, \(A = 2P\) and \(t = 7\).

- To find when it becomes 8 times:

- Use the relation \(A = P \times (1 + r)^t\) and \(A = 8P\).

- Since each doubling period is the same, doubling three times (from original to twice, then twice to 4, then 4 to 8) takes:

- \(7 \times 3 = 21\) years.

- Option 1: 14 years ? Only two doubling periods.

- Option 2: 21 years ? Correct, as it includes three doubling periods.

- Option 3: 28 years ? More than needed.

- Option 4: 35 years ? Too much time.

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