- Option : D
- Explanation : Let amount be Rs ‘A’

It becomes double = 2A in 9 years.

In next 9 years it again double i.e., becomes 2 × 2A = 4A

So in 9 + 9 = 18 years the amount becomes four times itself.

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- Option : A
- Explanation : 4 years – 3 years = 1 year

Thus, we can say that Rs 800 becomes Rs 840 in 1 year.

∴ Interest = Rs 840 – Rs 800 = Rs 40

For 1 year time period, Simple Intesest = Compound Interest

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- Option : C
- Explanation : 4 times in 6 years

So 16 times in 12 years

And 64 times in 18 years.

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