A trader use a weighing balance that shows 1250 g for a kilogram. He further marks- up his cost price by 20%. what is the profit percentage?

Let the cost price of one gram be Rs. 1, then the mark up price be Rs. 1.2 per g.
Now he sells 1000 g which seems to be 1250 g so he charges to a customer 1250 X 1.2 = Rs. 1500 for 1000 g (or Rs. 1000)
Thus his profit % 1500 -1000 / 1000 X 100 = 50 %