A wholesaler sells 20 pens at the marked price of 16 pens to a retailer. The retailer sells them at the marked price. Determine the gain percent of the retailer.

25%

According to question ,

Selling price of 20 pens = Marked price of 16 pens

Selling price of 1 pen  :   Marked price of 1 pen  = 16 : 20

= 4  :  5

Gain percent = \(\frac{5 - 4}{4}\) × 100%

= \(\frac{1}{4}\) × 100% 

= 25%