This seems to be a very easy problem but all the possible values seems to be correct when substituting and this is because when using algebra the equations cancel out.

How do you do it?





M is clearly 8 since 4=1-5+m-->m=8
But then we have:

(1) -4-5+n=y
(2) 10+7+n=e
(3) 10+y+23=4+e+3

3 equations and 3 unknowns but they cancel out, so I dont know how to solve it properly.

Thanks.

I don't think you're reading the table correctly. You basically take one thing from the top row and one thing from the left column - those two things add to the number in the cell where that row and column cross.

For example, x+4 = 1, y+4 = -5, z+4 = m

So I know that x = 3 and y = -9. That lets me figure out that e = 4, and then y + e = n or -9 + 4 = -5 = n.
Next, z + e = 10, or z + 4 = 10, therefore z = 6. z + 4 = m, so 6 + 4 = 10 = m

m+n = 10 + -5 = 5.

Like always you are right Stacey, I was not reading the table correctly, I was adding the entire row or colum. The way it really is makes it really easy, but sometime the GMAT has this, is not the problem but the way they show it.

Yeah, I was confused for a minute too, as I looked at that grid. :) In fact, the only way I felt really confident that it was supposed to be read the way I described was by doing the entire problem - then I knew I was doing it correctly.