Question

:
A pen costs twice that of an eraser. The pen and the eraser together
costs 39. (Take x to be the cost of an eraser.)​

Answer 1

Assume the cost of a Pencil is x, cost of Eraser is y and cost of Sharpener is z.

Then, cost of 2 pencils, 5 erasers and 7 sharpeners is Rs. 30. Thus,

2x + 5y + 7z = 30 …. (1)

Further, given cost of 3 pencils and 5 sharpeners is Rs. 15 (Assuming Rs. 1.50 is typo) more than 6 erasers. So,

3x + 5z = 6y + 15

3x - 6y + 5z = 15 …. (2)

Now, we need to find the difference of cost between 39 erasers + 1 sharpener and cost of 6 pencils. Thus, we need to compute 39y + z - 6x.

If we multiply Equation (1) by 3 and Equation (2) by -4 and then add these, we get:

-6x + 39y + z = 30.

So, the answer is Rs. 30.