Question

5 books and 7 pens together cost ₹79 whereas 7 books and 5 pens together cost ₹77. Find the

total cost of 1 book and 2 pens.​

Answer 1

Answer:

Let the cost price of 1 book be Rs. 'x' and the cost price of 1 pen be Rs. 'y' respectively.

So, according to the question.

⇒ 5x + 7y = 79  ...........(1)

⇒ 7x + 5y = 77  ...........(2)

Multiplying the equation (1) by 7 and equation (2) by 5, we get

⇒ 35x + 49y = 553.......(3)

⇒ 35x + 25y = 385.......(4)

Now, subtracting (4) from (3), we get.

⇒ 24y = 168

⇒ y = 168/24

⇒ y = 7

Substituting value of y = 7 in (1), we get.

⇒ 5x + 7*7 = 79

⇒ 5x = 79 - 49

⇒ 5x = 30

⇒ x = 6

So, cost of 1 book is Rs. 6  and cost of 1 pen is Rs. 7 

Now, cost of 1 book and 2 pens = 6 + (7*2)

= 6 + 14

= Rs.20

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Step-by-step explanation:

Answer 2

$\Large{\textbf{\underline{\underline{According\;to\;the\;Question}}}}$

Assumption

Cost of a book be ₹ p

Also,

Pen be ₹ t

So,

5p + 7t = 79 ....... (1)

7p + 5t = 77 ....... (2)

Now,

Multiply (1) by 5 also (2) by 7,

25p + 35t = 395 ………..… (3)

49p + 35t = 539 ………..… (4)

Now,

Subtract (3) from (4),

24p = 144

p = 144/24

p = 6

So,

Cost of book = ₹ 6

Substituting value of p in (1),

5p + 7t = 79

5 × 6 + 7t = 79

30 + 7t = 79

7t = 79 - 30

7t = 49

t = 49/7

t = 7

Hence,

Cost of pen = ₹ 7

Also,

Cost of 2 pens

= 2 × 7

= ₹ 14

Then,

Total cost of 1 book & 2 pens

= 6 + 14

= ₹ 20

Therefore,

Total cost of 1 book & 2 pens

= ₹ 20