Question

5 book and 7 pens together cost 79 whereas 7 book and 5 pen together cost 77 find the total cost of 1 book and 2 pen

Answer 1

Say, the cost of 1 book is = x rs.
and, cost of one pen is = y rs.

According to the question,
5x + 7y = 79
or, 5x x 7 + 7y x 7 = 79 x 7
or, 35x + 49y = 553........................(1)

Anew,
7x + 5y = 77
or, 7x x 5 + 5y x 5 = 77 x 5
or. 35x + 25y = 385......................(2)

(1) - (2)
or, 24y = 168
or, y = 7

so, 5x + 7 x 7 = 79
or, 5x = 30
or, x = 6

So, total cost of one book and one pen is-
= (x+y)
= 7 + 6 Rs.
= 13 Rs.

Hope this answer helped :-)

Answer 2

$\huge{\bf{\underline{\red{Solution :}}}}$

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

According to First Condition :

⇒ 5x + 7y = 79 ...................1) Equation

According to Second Condition:

⇒ 7x + 5y = 77 ............................2) Equation

So multiply by 7 to equation 1) and 5 to equation 2) and adding them :

⇒ 25x + 35y =395.......1) Equation

49x + 35y = -539........2) Equation

So -24x = -144

x = -144/-24

x = 6

Put the value of x in equation 1) :

⇒ 5 × 6 + 7y = 79

⇒ 7y = 79 - 30

⇒7y = 49

⇒y = 49/7

y = 7

So the total cost of one book and 2 pens

⇒ 6 + 2 × 7 = 20 Rupees ( Answer )