Question

5 books and 7 pens together cost 79 where as 7 books and 5 pens together cost 77.find total cost of 1 book and 2 pens

Answer 1

20 will be the cost of 1 book and 2 pen

Answer 2

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

Given 5x+7y=79--------->1
7x+5y=77---------->2
Adding both we get
12x+12y=156
X+y=13
Subtracting 1 from 2
2x-2y=-2
X-y=-1

X+y=13
X-y=-1

2x=12

X=6 ,y=7

Cost of one book=6
Cost of 2 pen =2×7=14
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