| If simple interest on any amount is equal to 30% of the principal in 6 yr, then after how many years simple interest will be equal to principal? |
A) 20 yr
B) 30 yr
C) 10 yr
D) 22 yr
Correct Answer: A
Solution :
| Let P be Rs. x. |
| \[\because \] SI = 30% of and \[x=Rs.\,\frac{3x}{10}\] and t = 6 yr |
| \[\therefore \] \[SI=\frac{P\times r\times t}{100}\] |
| \[\Rightarrow \] \[\frac{3x}{10}=\frac{x\times 6\times r}{100}\] |
| \[\Rightarrow \] \[r=\frac{3\times 100}{10\times 6}=5%\] |
| Now, P = Rs. x, SI = Rs. x and r = 5% |
| \[\therefore \] \[SI=\frac{P\times r\times t}{100}\] |
| \[\Rightarrow \] \[x=\frac{x\times 5\times t}{100}\] |
| \[\therefore \] \[t=\frac{100}{5}=20\,yr\] |
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