Question

5 books and 7 pens together cost Rs 79, whereas 7 books and 5 pens together cost Rs 77. Find the total cost of 1 book and 2 pens.

Answer 1

Suppose the cost of 1 book is Rs x and the cost of 1 pen is Rs y.

According to question

5x + 7y = 79

⇒ 5x + 7y – 79 = 0 ….(i)

and 7x + 5y = 11

⇒ 7x + 5y – 11 = 0 ….(ii)

Solving (i) and (ii), we get

Therefore, cost of 1 book and 2 pens = 6 + 2 x 7 

= 6 + 14 = Rs 20.