20.0185 expressed with 3 significant figures does not always mean to round to 3 figures.
Here is a good reference link http://www.usca.edu/chemistry/genchem/sigfig.htm
All non-zero digits are significant. All zeroes between two significant digits are significant. Zeroes not followed by a significant digit are not significant.
20.0185 has two zeroes and both are significant because they are between the 2 and the 1.
The 2 is significant because it is non-zero. Count the FIRST three significant digits from the left to the right. Do NOT round up or down.
This results in: 20.0
I'm afraid I disagree with the comment about not rounding. You should round. For example, suppose the number is 20.0815 (rather than 20.0185). In that case, to three significant figures the result is 20.1.
See http://mathematicsi.com/significant-figures/ for example.