Question

seven books and 5 pens cost Rs 410, whereas five books and seven pens
cost Rs.334 then the cost of three books and four pens would be

Answer 1

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

SOLUTION

GIVEN

• Seven books and 5 pens cost Rs 410

• Five books and seven pens cost Rs.334

TO DETERMINE

The cost of three books and four pens

EVALUATION

Let cost of one book = Rs x and cost of one pen = Rs y

So by condition 1

7x + 5y = 410 - - - - - - - (1)

By condition 2

5x + 7y = 334 - - - - - - - (2)

Multiplying both sides of Equation 1 by 7 we get

49x + 35y = 2870 - - - - - - (3)

Multiplying both sides of Equation 2 by 5 we get

25x + 35y = 1670 - - - - - - (4)

Equation 3 - Equation 4 gives

24x = 1200

⇒ x = 50

From Equation 1 we get

5y = 410 - 7x

⇒ 5y = 410 - ( 7 × 50 )

⇒ 5y = 410 - 350

⇒ 5y = 60

⇒ y = 12

∴ Cost of one book = Rs 50 and cost of one pen = Rs 12

Hence the required cost of three books and four pens

= Rs 3x + Rs 4y

= Rs 150 + Rs 48

= Rs 198

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