Acertain sum quadruples in 3 years at compound interest, interest being compounded annually. in how many years will it become 64 time itself?

ANSWER:  

In 9 years, amount becomes 64 times of itself.

SOLUTION:

Given, a certain sum quadruples in 3 years at compound interest, interest being compounded annually.  

We know that, When interest is compound annually:

Given that,

Principal = Rs.100%

Amount = Rs.400

Rate = r%

Time = 3 years

By substituting the values in above formula, we get,

--- eqn 1

If sum become 64 times in the time n years then,

--- eqn 2

Using equation (1) in (2), we get

Thus, n = 9 years by comparing on both sides.

Hence, in 9 years, amount becomes 64 times of itself.

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