By selling 20 pens, a shhopkeeper gained the selling price of 4 pens. Find the profit per cent.

By selling 100 pens, a shopkeeper gains the selling price of 40 pens. Find his gain per cent.

By selling 8 dozen pencils, a shopkeeper gains the selling price of one dozen pencils. Find his gain per cent.

On selling 100 pens, a man gains the selling price of 20 pens. The gain per cent is

By selling 50 pens, a shopkeeper lost the amount equal to the selling price of 10 pens. His loss per cent is __________.

On selling 100 pencils a man gains the selling price of 20 pencils. His gain per cent is