A dishonest shopkeeper sells sugar at a rate of Rs 45 per kg. The cost price of the sugar is Rs 40 per kg. Even after doing this, he tries to increase his profit by removing 100 gm from each packet of 1 kg. What is the gain percent of the shopkeeper?

25%

The cost price of 1 kg of sugar to the shopkeeper = Rs 40,

When he cheats by removing 100 gm from each packet of 1 kg, 

the cost price becomes 40 x $\frac{900}{1000}$ = Rs 36

                                   (using unitary method)

Profit per kg = Selling price per kg - Cost price per kg 

                   = Rs (45 - 36) = Rs 9      

Profit % = $\frac{9}{36}$ x 100 = 25%