The market price of a watch is Rs. 800. A shopkeeper gives two successive discounts and sells the watch…

After the first discount of 10%, the price is $800\times0.9=\text{Rs. }720$. The second discount takes it to Rs. 612, a cut of $720-612=\text{Rs. }108$. The second discount is worked out on Rs. 720, not Rs. 800: $\frac{108}{720}\times100=15\%$. A second discount of 10% would leave Rs. 648, so 10% is wrong.