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

Answer:

The total cost is RS 4322

Answer 2

Total cost of 1 book and 2 pens = Rs. 20

Step-by-step explanation:

Let cost of one book be x and cost of one pen be y.

Given:

5x + 7y = 79 -------------(1)

7x + 5y = 77 -------------(2)

(1)*7 will be 35x + 49y = 553 -----------(3)  

(2)*5 will be 35x + 25y = 385 -----------(4)

Subtracting (4) from (3), we get: 24y = 168

Therefore x = 168/24 = 7

Substituting in y = 7 equation 1, we get 5x + 49 = 79

Therefore x = 30/5 = 6

Hence solved. x = 6, y = 7

Therefore total cost of 1 book and 2 pens = Rs. 6 + 2 *Rs.7 = 6 + 14 = Rs. 20