Posted by Steve on Saturday, April 6, 2013 at 11:26pm.
If a and b are positive odd integers, then prove that one of (a+b)/2 and (ab)/2 are even or odd number. I mean in the above numbers one is odd and one is an even number.

Math  black_widow, Sunday, April 7, 2013 at 10:12am
Let a>b
a=2n+1+2k ,n,k is positive
b=2n+1
(a+b)/2=2n+1+k
(ab)/2=k
If k is odd,
then
(a+b)/2 is even
(ab)/2 is odd
If k is even,
(a+b)/2 is odd
(ab)/2 is even
The same method also applies if a<b
(However I assume that a,b are distinct number because if a=b, (ab)/2=0 but 0 is neither odd nor even) 
Math  to black_widow  Steve, Sunday, April 7, 2013 at 12:51pm
excuse me? 0 is an even number. The definition of even is that it leaves a zero remainder when divided by 2.

Math  black_widow, Friday, April 12, 2013 at 10:30pm
sorry about that....
I thought 0 is neither even nor odd....