A merchant marks an article 20% above cost price. Then he sells it at a discount of 20% . The sale gives him ?

Let the cost price = 100 unit
Now M.R.P = 120 units
$$\eqalign{ & {\text{Selling price}} \cr & = \frac{{120 \times 80}}{{100}} = 96 \cr & {\text{Loss}} = 100 - 96 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = 4 \cr & {\text{Loss }}\% = \frac{4}{{100}} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4\% \cr} $$