The selling price of 12 pens is equal to the cost price of 15 pens. Find the gain per cent.
Let the cost price of the pen be Re 1.
Cost price of 12 pens = Rs 12
SP of 12 pens = CP of 15 pens = Rs 15
Gain = SP - CP = Rs (15 - 12) = Rs 3
Gain% = 25%
RS Aggarwal (2017)