Rounding.

 

39.86 ≈ 39.9.

 

There are issues about rounding something like 39.85. We tell the students that we will round up. Bankers, however, who tend to lose money by always rounding up, alternate by looking at the previous number, rounding up or down if the number before the 5 is even or odd. Tell them that this will not be done in class.

 

Calculators do not use banker’s rounding.

 

Negative numbers are also rounded in the same way:

 

-39.86 ≈ -39.9