An article was sold for Rs. y after giving a discount of x%. Then, its list price is ?

Let the list price be Rs. z.
$$\eqalign{ & \therefore \left( {100 - x} \right)\% {\text{ of z}} = {\text{y}} \cr & \Rightarrow \left( {\frac{{100 - x}}{{100}}} \right) \times {\text{z}} = {\text{y}} \cr & \Rightarrow {\text{z}} = \left( {\frac{{100{\text{y}}}}{{100 - x}}} \right) \cr} $$