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General Form of a Linear Equation in Two Variables

5 books and 7...

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.

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Solution

Given:

(i) Cost of 5 books and 7 pens = Rs. 79.

(ii) Cost of 7 books and 5 pens = Rs. 77.

To find: Cost of 1 book and 2 pens.

Suppose the cost of 1 book = Rs x.

and the cost of 1 pen = Rs y.

According to the given conditions, we have

5x + 7y = 79

5x + 7y − 79 = 0 …… (1)

7x + 5y = 77,

5x + 7y − 77 = 0 …… (2)

Thus we get the following system of linear equation,

Hence, the cost of 1 book = Rs 6

and the cost of 1 pen = Rs 7.

Therefore the cost of 2 pen = Rs 14.

Total cost of 1 book and 2 pens = 14 + 6 = 20

Total cost of 1 book and 2 pens =

Hence total cost of 1 book and 2 pens =

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