Question #1c6ee

I would evaluate what is in implicit parentheses first. That means the numerator should be subtracted first, and then the result should be divided.

ADDITION/SUBTRACTION WITH SIG FIGS

#4.ul(85)_0 - 2.ul(34)# #"g"#

#=# #2.ul(51)# #"g"#

When you add/subtract, you keep the number of decimal places given by the number with the greatest uncertainty. #2.34# only has two decimal places, so you keep #bb2# decimal places.

The subscript #0# indicates the decimal place to drop, because #2.34# has one less decimal place and is therefore more uncertain by one decimal place.

MULTIPLICATION/DIVISION WITH SIG FIGS

Now, when you multiply/divide, you retain the least number of significant figures to account for the fact that your volume in #"mL"# has less significant figures than the mass in #"g"# with the greatest uncertainty.

#1.3# only has two significant figures, so you keep two significant figures to get:

#2.5_1/1.3 "g"/"mL"#

#= 1.9308 => color(blue)("1.9 g/mL"#

The subscript #1# indicates the significant figure to drop, since #1.3# has one less significant figure than #2.51# and is therefore more uncertain by one significant figure.

NOTE: You aren't necessarily less uncertain with more decimal places.

For example...

#0.00000ul(5)# has only one significant figure, but it has six decimal places.