Question

5 books and 7 pens together cost Rs.79 whereas 7 books and 5 pens cost Rs77 . find the total cost of one book and one pen

Answer 1

Say, the cost of 1 book is = x rs.
and, cost of one pen is = y rs.

According to the question,
5x + 7y = 79
or, 5x x 7 + 7y x 7 = 79 x 7
or, 35x + 49y = 553........................(1)

Anew,
7x + 5y = 77
or, 7x x 5 + 5y x 5 = 77 x 5
or. 35x + 25y = 385......................(2)

(1) - (2)
or, 24y = 168
or, y = 7

so, 5x + 7 x 7 = 79
or, 5x = 30
or, x = 6

So, total cost of one book and one pen is-
= (x+y)
= 7 + 6 Rs.
= 13 Rs.

Hope this answer helped :)

Answer 2

Answer:

Step-by-step explanation:

Solution:-

Let the cost of 1 book be x.

And the cost of 1 pen be y.

According to the Question,

⇒ 5x + 7y = 79 ..... (i)

⇒ 7x + 5y = 77 ......(ii)

Multiplying both Eq (i) with 7 and Eq (ii) with 5, we get

35x + 49y = 553 ...(iii)

35x + 25y = 385 ...(iv)

Substracting both the Eq (iii) and (iv), we get

⇒ 24y = 168

⇒ y = 168/24

⇒ y = 7

Putting y's value in Eq (i), we get

⇒ x = 6

Cost of book = x = 6

Cost of pen = y = 7

Total cost = 6 + 7 = Rs. 13

Hence, the total cost of 1 book and 1 pens is Rs. 13.