# The total cost of 6 books and 7 pens is 79 rupees and the total cost of 7 books and 5 pens is 77 ruppees. Find the cost of 1 book and 2 pens.

Let the cost of one book be 'x' rupees and cost of one pen be 'y' rupees.

Cost of 6 books and 7 pens = 79 Rs

6x + 7y = 79 eq.

Cost of 7 books and 5 pens = 77 Rs

7x + 5y = 77 eq.

Multiplying eq. by 5 both side, and Multiplying eq. by 7 both side, we get

30x + 35y = 395 eq.

49x + 35y = 539 eq.

Subtracting eq. from eq., we get

49x + 35y - 30x - 35y = 539 - 395

19x = 144 Using this in eq.  864 + 19×7y = 79×19

19×7y = 79×19 – 864 y = 5

& 6x + 7y = 79

6x + 35 = 79

6x = 44

x = 7

Hence, the cost of 1 pen & 2 books = Rs 1(y) + 2x

= 5 + 14 = Rs 19.

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