Question

A sum of money placed at compound interest doubles itself in 4 years. It will amount to eight times in ____.​

Answer 1

Answer:

12 years

Step-by-step explanation:

A sum of money placed at compound interest doubles itself in 4 years now for 4 times it will take 8 years and for 8 times 4×3=12 years.

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Answer 2

Answer:

12 yrs

Step-by-step explanation:

If a certain sum at compound interest becomes x times in n1 yr and

y times in n2 yr, then $x^{\frac{1}{n1} } = y^{\frac{1}{n2} }$

$2^{\frac{1}{4} } = 8^{\frac{1}{n2} }$

$2^{\frac{1}{4} } = 2^{\frac{3}{n2} }$

$\frac{1}{4} = \frac{3}{n2}$

n2= 12 years