Question

solve using elimination method

5 books and 7 pens together cost Rs 79, whereas 7 books and 5 pens together cost Rs 77. Find the cost of 1 book and 2 pens. obro
Fund that of.
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Answer 1

Answer:

Let the cost of 1 book =x

And the cost of 1 pen =y

⇒5x+7y=79

⇒7x+5y=77

Equation (1) × 7 : 35x+49y=79×7

Equation (2) × 5 : 35x+25y=77×5

Subtract two equations ;

⇒24y=168

⇒y=7

⇒x=6

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

Answer 2

Answer:

Cost of 1 book = 6

Cost of 1 pen = 7

Explanation:

Let cost of 1 book= x

Let cost of 1 pen= y

Given, 5 books and 7 pens cost 79.

i.e. 5x+7y=79 ---1

Given, 7 books and 5 pens cost 77.

i.e. 7x+5y=77 ---2

Multiplying equation 1 by 5 and equation 2 by 7

25x+35y= 395 ---3

49x+35y=539 ---4

Subtracting equation 3 from equation 4

 49x+35y=539 -(25x+35y=395)

on simplifying,

24x = 144

x = 144/24

x = 6

5x+7y=79

5 x 6 +7y=79

30+7y=79

7y=49

y = 7