Question

Cost of 5 books and 7 pens is Rs 79 and cost of 7 books and 5 pens is Rs 77 .Then find the cost of 2 books and 3 pens​

Answer 1

Answer:

Let the cost of 1 book =x

And the cost of 1 pen =y

⇒5x+7y=79

⇒7x+5y=77

Equation (1) × 7 : 35x+49y=79×7

Equation (2) × 5 : 35x+25y=77×5

Subtract two equations ;

⇒24y=168

⇒y=7

⇒x=6

Total cost of 1 book and 2 pens =x+2y=6+14=20

Answer 2

Answer:

Let price of a book = Rs. X

Price of a pen = Rs.Y

5X + 7Y = 79 …(1) × 7

7X + 5Y = 77…(2) × 5

35X + 49Y = 553…(3)

35X + 25Y = 385..(4)

Subtract equation (3) from (4)

24Y = 168

Y = 7

Put value of Y in equation (1)

5X + 7×7 = 79

5X = 79 - 49

5X = 30

X = 6

Cost of a book = Rs.6

Cost of 2 pens = Rs.14

Total Rs.20