The marked price of a watch was Rs. 720/-. A man bought the same for Rs. 550.80, after getting two successive discount, the first art 10%. What was the second discount rate?

15%
Marked price = Rs. 720
Actual price = Rs. 550.80
First discount = 10%
Let the second discount be x%
Then, we can write 720(1 – 0.10)(1 – 0.01x) = 550.80
$latex =>$720 $latex \times$ 0.9(1 – 0.01x) = 550.80
$latex =>$648(1 – 0.01x) = 550.80
$latex => 1-0.01x=\frac{550.8}{648}&s=1$
$latex =>0.01x=1-\frac{550.8}{648}&s=1$
$latex =>x=\frac{1-0.85}{0.01}&s=1$
$latex =>x=0.15\times 100$
$latex =>x=15$
Hence option [C] is the right answer.