Solution: 1st method : Let C.P. of each apple be Re. 1.
then, C.P. of 18 apples = Rs. 18. So, S.P. of 15 apples = Rs. 18.
.'. Gain% = (3/15 * 100) = 20%.
2nd Method : Cost price of x apples is equal to the selling price of y apples then the loss or gain percent is :
(x - y)*100/y according as - or + sign.