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Number of Equations and Variables in DS

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by gmatpup » Wed Nov 16, 2011 8:13 am
Hi guys

I am hoping someone can clarify this for me. I know that if we have an equal amount or more equations compared to variables then it is SUFFICIENT. But does this mean we use the equation we form from the question (if possible)? Or do we just use the equations from the statement?

Thanks so much :)!!!
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by GmatMathPro » Wed Nov 16, 2011 10:35 am
gmatpup wrote:I know that if we have an equal amount or more equations compared to variables then it is SUFFICIENT.
Be careful with shortcuts like this. For example, if the question is "If 2x+3y=6, what is x?" and one of the statements is "4x+6y=12", it may look like you have two equations, but the second equation is just the same equation from the given multiplied by 2. You really need two DISTINCT equations to solve for the unknowns.

Plus, there can be cases where you have just one equation and two unknowns but it could still be sufficient if there are other conditions, such as that the unknown values are restricted to integer values. For example, if we know that 2x+3y=10 and x and y are positive integers, then only x=3, y=2 solves the equation, so we wouldn't need a second equation.

To answer your question, though, you should always include any information, equations or otherwise, that you can deduce from the question when trying to determine sufficiency.
Pete Ackley
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