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I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...

I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...

Have you tried to solve these 2 equations?

When you add u-v+w=20 and u+v-w=16 you'll get u=18 and if you substitute the value of u in these two equations you'll get: for 1. 18-v+w=20 --> w-v=2 and for 2. 18+v-w=16 --> w-v=2, so two identical equations, thus you won't be able to solve for w, v or for w+v.

Statement to be sufficient you need ndistinct linear equations for n variables. _________________

I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...

Using the information in 1) it is possible to solve for v and w in 2). However, in order for D to be correct, we would need to be able to solve for v and w using only the information in 2). Since 1) is sufficient and 2) is insufficient alone, the answer is A. _________________

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Re: Is 20 the average? [#permalink]
20 Jul 2010, 12:14

I think as people have pointed out already, you need to make sure you actually know that the equation is solvable. Don't just think that since it simplifies to two equations with two variables you'll be able to solve it. It needs to be two distinct equations.