If X + Y = 12, Y + Z = 13 and X + Z = 25, then X + Y + Z = ?

Method: Add the three given equations and simplify.

1. Add the equations: (X + Y) + (Y + Z) + (X + Z) = 12 + 13 + 25

2. Simplify the left side: 2(X + Y + Z) = 50

3. Divide both sides by 2: X + Y + Z = 25

Final answer: 25