The marked price of watch was Rs. 820. A man bought the same for Rs. 570.72 after getting two successive discounts of which the first was 20%. The rate of second discount was -

A. 12%

B. 13%

C. 15%

D. 18%

Answer: Option B

Solution(By Examveda Team)

Let the second discount rate be x%
Then,
(100 - x)% of 80% of 820 = 570.72
$$\eqalign{ & \Rightarrow \frac{{\left( {100 - x} \right)}}{{100}} \times \frac{{80}}{{100}} \times 820 = 570.72 \cr & \Rightarrow \left( {100 - x} \right) = \left( {\frac{{57072}}{{8 \times 82}}} \right) = 87 \cr & \Rightarrow x = 13 \cr} $$
∴ Second discount rate = 13%