Question

if the selling price of five pens is equal to the cost price of four pens then the gain or loss% is=? ​

Answer 1

Gain percent = (Gain / C.P) × 100

How much did you gain by selling 5 pens? You gained the actual C.P of one of the pens.

So, your gain = C.P. of 1 pen

So, gain percent = (C.P/4×C.P)×100 = 25%