1.5 + 1 = 2.5 ----> was that number round down anyhow ? If you round it .. it should be UP .. not DOWN or was it that in the code the .5 was dropped ?
There's no mathematical rule that says how numbers should be rounded off. Rounding numbers is a social convention for expressing approximate numbers.
Yes, rounding numbers are a convention known throughout the history. Precisely, rounding number 5 UP is also a convention.
As far as I can tell under D&D 5E rules, you ALWAYS round down any time you get a fraction. Even if the fraction is 0.9, you round it down.
Please quote that rule here. And if true, then, it means D&D doesn't understand math.
To the point though, the decimal is within the operation and you don't round numbers before the end of the operation, and that IS a mathematic rule, hence why you get 10 in google.
