Question

o questions
I The total cost of 5
books and 7 pers
is 79 rupees and the total cost
7 books and 5 pens
is 77 rupees
Find the cost
of 2 books and
1.
pens.​

Answer 1

Answer:

19

Step-by-step explanation:

let us think one book as x and one pen as y

so,

5x + 7y = 79.......(i)

7x + 5y = 77........(ii)

now we will multiply equation (i) by 7 and (ii) by 5.

(5x×7) + (7y×7) = 79×7

=> 35x + 49y = 553......(iii)

(7x×5) + (5y×5) = 77×5

=> 35x + 25y = 385.....(iv)

then subtract (iv) from (iii).

(35x + 49y = 553) - (35x + 25y = 385) =>

35x-35x + 49y-25y = 553-385 =>

24y = 168

We will solve the equation.

24y = 168 =>

y = 168÷24 =>

y = 7

cost of pen = 7

now putting y's value in equation (i) to find x.

5x+7y = 79 =>

5x + 7(7) = 79 =>

5x + 49 = 79 =>

5x = 79-49 =>

5x = 30 =>

x = 30÷5

x = 6

cost of book = 6

at the end cost of 2 books and 1 pen =

2(6) + 7 = 12+7

= 19

Hence the cost of 2 books and 1 pen = 19.

you can check all equations and answers yourself.

hope it helps.