| Rekha invested a sum of Rs. 12000 at 5% per annum compound interest. She received an amount of Rs. 13230 after n yr. Find n. [SSC (CPO) 2014, SSC (CGL) 2014] |
A) 2.8 yr
B) 3.0 yr
C) 2.5 yr
D) 2.0 yr
Correct Answer: D
Solution :
(d)| Rekha's investment, P = Rs. 12000 |
| Rate of interest, R = 5% per annum |
| Amount received after n yr, A = Rs. 13230 |
| By the formula of compound interest\[A=P{{\left[ 1+\frac{R}{100} \right]}^{n}}\] |
| \[\Rightarrow \]\[13230=12000{{\left[ 1+\frac{5}{100} \right]}^{n}}\]\[\Rightarrow \]\[\frac{13230}{12000}={{\left[ \frac{21}{20} \right]}^{n}}\] |
| \[\Rightarrow \]\[\frac{441}{400}={{\left( \frac{21}{20} \right)}^{n}}\]\[\Rightarrow \]\[{{\left( \frac{21}{20} \right)}^{2}}={{\left( \frac{21}{20} \right)}^{n}}\] |
| On comparing, we get \[n=2yr\] |
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