I have to go with the 'calculation is wrong' group. While the integer vs decimal part is also a problem, the first and foremost problem is the calculation is dead wrong and would never provide a correct result. Now if part of the intention was to have an incorrect calculation as a distraction from the integer vs decimal piece of the puzzle then bravo, point taken.
However a simpler question to make the same point would be more like
why does select 5/10 not = .5?
Just saying....