The total cost of two different priced schools is Rs.60. If the cost of 1 cheap pen is ₹ 1.50 and the cost of an expensive pen is ₹ 2, then how many expensive pens were bought?

Solution: Let x costlier pens and (35-x) cheaper pens be purchased.

Now since cost of 1 expensive pen = ₹ 2

Therefore, cost of x expensive pen = ₹ 2x

Therefore (35-x) cost of (35-x) cheap pen=₹ 1.5×(35-x)=₹ 1.5(35-x)

According to Question,

Total cost of all cheap and expensive pens = ₹60

Therefore, cost of x expensive pen + (35-x) cost of cheap pen=₹60

or 2x+1.5×(35-x)=60

⇒2x+1.5×35-1.5x=60

⇒ 2x+52.5-1.5x=60

⇒0.5x=60-52.5

⇒0.5x=7.5

⇒ x=7.5/0.5

Therefore, x=15

Hence 15 expensive pens were bought.