Question

5 textbooks and 7 notebooks cost * 550 whereas 7 textbooks and 5 notebooks
cost 650. What is the cost of 1 textbook and 1 notebook?
(1) 120
(2) 80
(3) 100
(4) * 110​

Answer 1

Answer:

(3) ₹100

Step-by-step explanation:

Let us think 1 textbook as x and 1 notebook as y, so

5x + 7y = ₹550....(i)

7x + 5y = ₹650.....(ii)

now we will multiply equation (i) by 7, and equation (ii) by 5 :-

(5x×7) + (7y×7) = 550×7 =

= 35x + 49y = 3850.......(iii)

(7x×5) + (5y×5) = 650×5 =

= 35x + 25y = 3250.......(iv)

now we will subtract equation (iii) to (iv) :-

=> (35x+ 49y = 3850) - (35x 25y = 3250 )

=> 35x-35x +49y-25y = 3850-3250

=> 24y = 600

=> y = 600÷24

=> y = 25

Hence rate of a notebook = ₹25

now putting y's value in equation (i) :-

=> 5x+7y = 550

=> 5x + (7×25) = 550

=> 5x +175 = 550

=> 5x = 550-175

=> 5x = 375

=> x = 375÷5

=> x = 75

Hence rate of a textbook = ₹75

cost of 1 textbook and 1 notebook = ₹25+₹75 =

₹100

you can check the value yourself.

hope it helps.