Question

Word Problem:- 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.

Class 10th

NO SPAMMING

Answer 1

★Hey mate ★✋

You have asked a superb question. Here is your answer.
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If, 1 book => x
so, 5 books => 5x
7 books => 7x

Again, if, 1 pen => y
7 pens => 7y
5 pens => 5y

According to the question,
5x + 7y = 79 ---- (1)
7x + 5y = 77 ----(2)

Now, equation (1) is multiplying by 7 & equation (2) is multiplying by 5 :

so, 35x + 49y = 553
35x + 25y = 385
_(-)____(-)_____(-)_______
24y = 168 [ by substraction ]
=> y. = (168/24)
=> y. = 7
=> 2y = 14 [Answer]

Now, putting the value of y in equation (1),
5x + (7×7) = 79
=>5x + 49 = 79
=>5x. = (79-49)
=> x. = (30\5)
=> x. = 6 [Answer]

So, the cost of 1 books is 6 & the cost of 2 pens is 14.
Total cost :(14+6)=20 [Answer]

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Hope that it will help you,friend :)

Answer 2

hey !!!!

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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,

$5x + 7y - 79 = 0 \: \: \: and \\ 5x + 7y - 77 = 0$
$\frac{x}{ - 539 + 385} = \frac{ - y}{ - 385 + 553} = \frac{1}{25 - 49 } \\ \\ \frac{x}{ - 144} = \frac{ - y}{ - 168} = \frac{1}{ - 24 } \\ \\ x = \frac{ - 144}{ - 24} \\ \\ x = 6$

$\frac{ - y}{ - 385 + 553} = \frac{1}{25 - 49} \\ \\ \frac{ - y}{168} = \frac{1}{ - 24} \\ \\ y = \frac{ - 168}{ - 24} \\ \\ y = 7$


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 = Rs. 20

Hence total cost of 1 book and 2 pens = Rs 20

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Hope u got it !!!
Cheers

# Nikky