| A sum amounts double in 8 yr by simple interest. Then, the rate of simple interest per annum is [SSC (CPO) 2014] |
A) 10%
B) 12.5%
C) 15%
D) 20%
Correct Answer: B
Solution :
(b)| Let the amount be Rs. x. According to the question, After 8 yr, amount \[=\text{Rs}\text{. 2}x\] |
| Now, simple interest \[(SI)=2x-x=x\] |
| Again, by the formula, \[SI=\frac{P\times r\times t}{100}\]\[\Rightarrow \]\[x=\frac{x\times r\times 8}{100}\] |
| \[\Rightarrow \] \[r=\frac{100}{8}=12.5%\] |
| Alternate Method |
| Here, \[t=8\,\,yr,\]\[n=2\] |
| \[\therefore \]Required rate per cent \[=\frac{n-1}{t}\times 100\]% \[=\frac{2-1}{8}\times 100\]% \[=\frac{1}{8}\times 100=12.5\]% |
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