I'm sure there's an algebraic way to solve this, but this is just an intuitive way I found...
If you look in the X column, you see that X+4=1, X+E=7, and X+F=2. Since this is simple addition, there will be a constant change between figures as you go across a row.
Start in the X column and see that the number 1 increases to 7; an increase of 6. It then decreases from 7 to 2; a decrease of 5. Follow this rule across the rows, and you'll get your answer.
Y column: -5+N must represent an increase of 6. -5+6=1, so N=1.
Z column: m+6=10, so M=4.
N+M=1+4=5
I hope this helps!
Please help with this PS
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Source: Beat The GMAT — Problem Solving |

















