A man buys a number of pens for Rs. 180. If he had bought 3 more pens for the same amount, each pen would have cost him Rs. 3 less. How many pens did he buy ?

Answer

12 pens

Explanation

Suppose he bought x pens.
`:." "(180)/(x)-(180)/((x+3))=3implies(1)/(x)-(1)/(x+3)=(1)/(60)impliesx(x+3)-180=0`
`:." "x^(2)+15x-12x-180=0.`