Question

The total cost of 6 books and 7 pens is 70 rupees and the total cost of 7 books and 5
number
is 77 rupeess. Find the cost of l book and 2 pens.​

Answer 1

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Proper Question:

The total cost of 6 books and 7 pens is 70 rupees and the total cost of 7 books and 6 number is 77 rupees. Find the cost of l book and 2 pens?

Given:

Total cost of 6 books and 7 pens is 79 rupees and Total cost of 7 books and 6 pens is 77 rupees

To find:

Cost of 1 book and 2 pens = ?

Solution:

Let x be the cost of 1 book and y be the cost of 1 pen

As 6 books and 7 pens cost Rs 70

6x + 7y = 79 ----(1)

As 7 books and 6 pens cost Rs 77

7x + 6y = 77 ----(2)

Subtracting (1) and (2)

6x + 7y - ( 7x + 6y) = 79 - 77

6x + 7y - 7x - 6y = 2

6x - 7x + 7y - 6y = 2

y - x = 2 -----(3)

Adding (1) and (2)

6x + 7y + 7x + 6y = 79 + 77

13x + 13y = 156

Dividing the above equation with 13

x + y = 12 ----(4)

Adding (3) and (4)

y - x + x + y = 2 + 12

2y = 14

y = 14/2

y = 7

Substituting value of x in equation (3)

y - x = 2

7 - x = 2

7 - 2 = x

x = 5

As we have to find cost of 1 book and 2 pens

= x + 2y

= 5 + 2 × 7

= 5 + 14

= 19

Required answer:

Thus, cost of 1 book and 2 pens is Rs 19

Knowledge booster:

# While solving such questions you can keep any variable. Solving using variable (x, y..) make calculation easier

# While substituting value, you can use any equation

# Solve more such questions to get good hold on it