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# Doris and Edward both collect stamps. If Doris gives Edward 72 stamps,

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Re: Doris and Edward both collect stamps. If Doris gives Edward 72 stamps, [#permalink]
Top Contributor
KritiG wrote:
Solving the eqn is very time comsuming!
I know that we cant use the plug in method as the question asks us about difference between two variables.
Any other shortcuts?

Actually speaking, in the exam, our first thought would be to solve the equations and get the individual values.

What we need to realize is that we want D - E, so we should try to see if we can do a simple operation to get this value without having to get individual values.

The first equation is D - 72 = 4(E + 72)

So D - 4E = 360 ... (1)

The second equation is D - 129 = 3(E + 129) = 3E + 516

D - 3E = 516 ... (2)

Equation (2) * 3 - Equation (1) * 2 gives us 3(D - 3E) - 2(D - 4E) = (516 * 3) - (360 * 2)

3D - 9E - (2D - 8E) = 1548 - 720

D - E = 928

Option E

Arun Kumar
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Re: Doris and Edward both collect stamps. If Doris gives Edward 72 stamps, [#permalink]
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Re: Doris and Edward both collect stamps. If Doris gives Edward 72 stamps, [#permalink]
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