Question

Average cost of 8 pens and 5 pencils is rs 25. while the average cost of 4 pens and 7 pencils is rs 21. what is the total cost of 18 pens and 18 pencils?

Answer 1

Let The cost of 1 pen be x and cost of 1 pencil be Y.
So,

$\frac{8x + 5y}{13} = 25 \\ 8x + 5y = 325..............(1)$

And Now,

$\frac{4x + 7y}{11} = 21 \\ 4x + 7y = 231..............(2)$

Equalising (1) & (2)
8x+5y = 325 -------(3)
4x+5y = 231 --------(4)
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By Subtracting (4) from (3)
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8x+5y-(4x+5y) = 325-231
8x+5y-4x-5y = 94
(8-4)x = 94
4x = 94
X = 23.5

Cost of 1 Pen = ₹ 23.5

Putting the value of x in equation (1)
We have,

$8 \times (23.5) + 5y = 325 \\ 188.0 + 5y = 325 \\ 5y = 325 - 188 \\ 5y = 137 \\ y = \frac{137}{5} \\ y = 27.4$

Value of 1 pencil is ₹ 27.4.

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