Heh, well, to be fair, the question is incredibly vague.
It's "Why do I get the result I get?"
The are many factors that combine to get this particular result.
Yes, it is true that the behavior of integer division contributes to this result (i.e., the result would be different if DiscountPercentage were not an integer and DiscountPercentage/100 returned something non-zero, or if the literal were 100.0).
However, the same is true of the calculation being incorrect. If the calculation were correct, the results would also be different.
You need both of the integer division behavior and this particular incorrect calculation to get these results.
Each is only a partial explanation of why we get the particular results we get.
If the question had been "Why do I get these values for FinalCost, instead of 50.00, 199.95, and 1099.90 (my expected results)?" Then absolutely, the current answer would be the only correct one.
As it stands, though it's a poor question/answer set.