Management Aptitude Test Dec 2013 Paper

(b) Let the rate per cent of bill be r% per annum.
Let the amount of bill be ₹ A.
Then, according to the question
A = $\frac{1200\left(100+\frac{7}{12}\mathit{r}\right)}{100}$ = 12 $\left(100+\frac{7}{12}\mathit{r}\right)$    .... (i)
A = $\frac{1016}{100}\left(100+\frac{5}{2}\mathit{r}\right)100$ = 10.16 $\left(100+\frac{5}{2}\mathit{r}\right)$   .... (ii)
From Eqs. (i) and (ii), we get
12 $\left(100+\frac{7}{12}\mathit{r}\right)$ = 10.16 $\left(100+\frac{5}{2}\mathit{r}\right)$
⇒ 1200 + 7r = 1016 + 25.4r
⇒ 18.4r = 184
∴ r = 10%
Hence, rate per cent of the bill is 10% per annum.