9.58 g·mL⁻¹; 13 mL
In division problems, your answer can have no more significant figures than the number with the fewest significant figures.
98.66 g/10.3 mL = 9.578 640 777g·mL⁻¹ (by my calculator)
There are four significant figures in 98.66, but only three in 10.3.
You must round off your answer to three significant figures.
9.578 640 777 → 9.58 (to three significant figures)
∴ 98.66 g/10.3 mL = 9.58 g·mL⁻¹
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When adding values, you must round your answer to the same "place" as the measurement with its last significant figure furthest to the left.
4.5 mL
+5.66 mL
+3 mL
13.16 mL
The “3” in “3 mL”has its last significant figure furthest to the left, so you round off the number to the “units" place. That's the last column that the measurements share.
13.16 → 13 (rounded to the “units” place)
∴ 4.5 mL + 5.66 mL + 3 mL = 13 mL
