Question

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

Answer 1

Let the total number of pens be x.
According to the question: 

`80/x-80/(x+4)=1` 

⇒`(80(x+4)-80x)/((x(x+4) `=1 

⇒`320=x^2+4x` 

⇒`x^2+4x-320=0` 

⇒`x^2+(20-16)x-320=0` 

⇒`x^2+20x-16x-320=0` 

⇒`x(x+20)-16(x+20)=0` 

⇒`(x+20)(x-16)=0` 

⇒`x=-20  or  x=16` 

The total number of pens cannot be negative; therefore, the total number of pens is 16.