An addition table is simply a matrix whereby you take the numbers on the edge (the first collumn) and sum with the numbers in the top row, placing their sum where the two numbers intersect on the chart. For example, in the chart given, the first number on the collumn is 4 and the first variable on the top row is x. You see that the "answer" is given as 1. So, 4 plus what number will give you 1? Answer = -3. You then go about filling in the missing blanks until you have a chart that looks like this:

+ -3 -9 0
4 1 -5 4
10 7 1 10
5 2 -4 5

therefore, m= 4 and n = 1 and m+n = 5. Sorta like that old game battleship...

hope this helps.

actually it only looks tough..

from the table 4+x=1, x=-3
e+x=7
e=7-x=7-(-3)=10

e+z=10, z=0

4+z=m, m=4
4+y=-5,y=-9
e+y=n
10-9=n
n=1
m+n=5

and dude, you have only one day left..why don't you stop solving new questions?
good luck!!!

I just wanted to squeeze through all the questions i got wrong in my last gmat prep so i thought id just post em' here. Yeah this was more of a puzzle then a math questions and i got lost in creating simultaneous equations instead. I have seen gmat prep putting a strong emphasis on logic in math too. Maybe i should be open for surprises like these!

Tks everyone for the solns!