(i) Add `73.24 mL` and `20.3 mL` (ii) Subtract `21.2342 g` foru `27.87 g`
Strategy: We first ensure that the quatities to be added or subtracted are expressed in the same units. We carry out the adition or subtraction. Then we follow rule 1 to express the answer to the correct number of significant figures, i.e., in the final answer, the number of right of the decimal point should be equal to the number of digits after the decimal point.

Explanation

(i) `{:(73.24mL, larr "Two digits after the decimal point"),(+20.30 mL,larr "One digit after the decimal point"),(bar(93.54 mL),larr "Reported as 93.5 mL"):}`
(ii) `{:(27.8700 g, larr "Two digits after the decimal point"),(-21.2342 g,larr "One digit after the decimal point"),(bar(6.6358 g),larr "Reported as 93.5 mL"):}`