What is the nearest whole number to 4.5?

Answer 1

I would say 4.

Most schools teach you to always round up 5 (to 5 in this case). That is a simple rule to teach to young children but what it overlooks is that the process introduces an upward bias. You do not need to be an expert mathematician to figure out that if

for 1,2,3 and 4 you round down

for 5,6,7,8 and 9 you round up,

(for 0 you don't need rounding.

Then for a random lot of numbers you will be rounding up 5/9 of the time and rounding down only 4/9. Not exactly unbiased, is it?

One solution to this is to round 5 so that the last significant digit is even. All else remains as above. The procedure is only slightly more complicated but at least it is unbiased!