by selling 90 pens , a trader gains the cost of 15 pens . find his gain percentage ?
"let the cp of each pen be rs . 1 . cp of 90 pens = rs . 90 profit = cost of 15 pens = rs . 15 profit % = 15 / 90 * 100 = 16.66 % answer : a"
multiply(divide(15, 90), const_100)