the total cost of 5 books and 7 pens is 79 rupees and the total cost of 7 books and 5 pens is 77 rupees. Find the cost of 1 book and 1 pan.
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Answer:
Given that ;
Total cost of 5 books and 7 pens = Rs 79
Total cost of 7 books and 5 pens = Rs 77
Let
The Books be x
The Pens be y
Total cost of 5 books and 7 pens = Rs 79
5x + 7y = 79 ---- ( 1 )
Total cost of 7 books and 5 pens = Rs 77
7x + 5y = 77 ----- ( 2 )
Equation ( 1 ) × 5
25x + 35y = 395
Equation ( 2 ) × 7
49x + 35y = 539
Elimination Method :
25x + 35y = 395
49x + 35y = 539
------------------------
- 24x = - 144
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- 24x = - 144
x = 144 / 24
x = 6
Hence ;
Cost of 1 Book ( x ) = Rs 6
Substitute x value in Equation ( 1 ) :
5x + 7y = 79
5 ( 6 ) + 7y = 79
30 + 7y = 79
7y = 79 - 30
7y = 49
y = 49 / 7
y = 7
Hence ;
Cost of 1 Pen ( y ) = Rs 7
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