For non-negative integers $a$ and $b,$ where $a \ge 2$ and $b \ge 2,$ simplify (a + b)/2 - a/2 - b/2
First, we can factor out a 21 from all the terms:
(a + b)/2 - a/2 - b/2 = \frac{1}{2} (a + b - a - b)
Then, we can combine the a and b terms:
\frac{1}{2} (a + b - a - b) = \frac{1}{2} \cdot 0 = \boxed{0}
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