| A sum of money placed at compound interest doubles itself in 5 yr. It will amount to eight times itself at the same rate of interest in |
A) 15 yr
B) 12 yr
C) 10 yr
D) 20 yr
Correct Answer: A
Solution :
| According to the question, |
| \[2P=P{{\left( 1+\frac{R}{100} \right)}^{5}}\]\[\Rightarrow \]\[{{\left( 1+\frac{R}{100} \right)}^{5}}=2\] |
| On cubing both sides, we get |
| \[{{\left[ {{\left( 1+\frac{R}{100} \right)}^{5}} \right]}^{3}}={{2}^{3}}\]\[\Rightarrow \]\[{{\left( 1+\frac{R}{100} \right)}^{15}}=8\] |
| \[\therefore \] Time = 15 yr |
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