Question

4. 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.


( Ans: 20 )

Class 10

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Answer 1

Let the cost of 1 book be x and cost of 1 pen be y(in rupees)

Then ATQ,

Case 1, (5x + 7y = 79)5

=> 25x + 35y = 395 ---------(1)

Case 2 , (7x + 5y = 77)7

=> 49x + 35y = 539 ----------(2)

Substract (1) from (2)

=> (49x + 35y) - (25x + 35y) = 539 - 395

=> 24x = 144

=> x = 6

Thus using x in original (1)

=> 5x + 7y = 79

=> 30 + 7y = 79

=> 7y = 49

=> y = 7

To Find : Cost of 1 book and 2 pen

= 6 + 2(7)

= 6 + 14

= 20

Thus, the cost of 1 book and 2 pen is Rs.20

Answer 2

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Difficulty Level : Average

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Let the cost of 1 book be x and cost of 1 pen be y(in rupees)

Then ATQ,

Case 1, (5x + 7y = 79)5

=> 25x + 35y = 395 ---------(1)

Case 2 , (7x + 5y = 77)7

=> 49x + 35y = 539 ----------(2)

Substract (1) from (2)

=> (49x + 35y) - (25x + 35y) = 539 - 395

=> 24x = 144

=> x = 6

Thus using x in original (1)

=> 5x + 7y = 79

=> 30 + 7y = 79

=> 7y = 49

=> y = 7

To Find : Cost of 1 book and 2 pen

= 6 + 2(7)

= 6 + 14

= 20 <<<<<<<<<<<<< Answer

Thus the cost of 1 book and 2 pen is Rs.20

_____________________

Hope this helps ✌️

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