If on a marked price, the difference of selling prices with a discount of 30% and two successive discounts of 20% and 10% is Rs. 72, then the marked price in Rs. is

Let the M.P. be Rs. x
Then,
(90% of 80% of x) - (70% of x) = 72
$$\eqalign{ & \Rightarrow \left( {\frac{{90}}{{100}} \times \frac{{80}}{{100}} \times x} \right) - \left( {\frac{{70}}{{100}} \times x} \right) = 72 \cr & \Rightarrow \frac{{72}}{{100}}x - \frac{{70}}{{100}}x = 72 \cr & \Rightarrow \frac{2}{{100}}x = 72 \cr & \Rightarrow x = \left( {\frac{{72 \times 100}}{2}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\, = 3600 \cr} $$