A dishonest grocer sells rice at a profit of 10% and uses weight which are 20% less than the marked weight. The total gain earned by him will be = ?

According to the question,
Grocer use 20% less weight
= 1000 - 200
= 800 gm.
$$\eqalign{ & {\text{The profit }}\% \cr & = \frac{{200}}{{800}} \times 100 \cr & = 25\% \cr & {\text{Then total profit }} \cr & = 10 + 25 + \frac{{25 \times 10}}{{100}} \cr & = 37.5\% \cr} $$