Q. 84.7( 4 Votes )

The cost of 5 pens and 8 pencils is Z 120, while the cost of 8 pens and 5 pencils is Z 153. Find the cost of 1 pen and that of 1 pencil.

Class 10th RS Aggarwal - Mathematics 3. Linear Equations in Two Variables

Answer :

Let us assume the cost of 1 pen is Rs x and that of pencil is Rs y

According to the question, we have

5x + 8y = 120 …(i)

8x + 5y = 153 …(ii)

Now, adding both the equations we get:

13x + 13y = 273

13 (x + y) = 273

x + y = 21 …(iii)

Now, by subtracting (i) from (ii) we get:

3x – 3y = 33

x – y = 11 …(iv)

By adding (iii) and (iv), we get:

2x = 32

Putting the value of x in (iii), we get

16 + y = 21

y = 21 – 16

y = 5

∴ The cost of 1 pen is Rs. 16 and that of 1 pencil is Rs. 5

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