If the selling price of 10 pens is equal to the cost price of 14 pens, find gain per cent.
Let the cost of each pen be Rs. 1
CP of 10 pens = Rs. 10
SP of 10 pens = CP of 14 pens = Rs. 14
Gain = SP - CP = 14-10= Rs. 4
RS Aggarwal (2017)