1/2 is wrong, I put it on my exam and got it wrong:/
6 numbers per cube
if one is a 1, then the other one has to be a 2, 4 or 6 to be an odd sum
1+2=3, 1+4=5,1+6=7
since there are 3 numbers you can get that would be a 3/6 ( reduce to 1/2) probability
so 1/2 probability
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