A dishonest shopkeeper professes to sell goods at his cost price but uses a false weight of 950 gms, for each kilogram. His gain percentage is = ?

In this type of question we can find the profit % by
$$\eqalign{ & {\text{ = }}\frac{{{\text{Less quantity}}}}{{{\text{Quantity given to customer}}}} \cr & {\text{According to the question,}} \cr & {\text{Less quantity}} = \left( {1000 - 950} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 50 \cr & {\text{Quantity given to customer}} = 950 \cr & {\text{Profit }}\% = \frac{{50}}{{950}} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{100}}{{19}}\% \cr} $$