Mass of grocer’s box = 2.300 kg

Mass of gold piece **I** = 20.15g = 0.02015 kg

Mass of gold piece** II** = 20.17 g = 0.02017 kg

Total mass of the box = 2.3 + 0.02015 + 0.02017 = 2.34032 kg

In addition, the final result should retain as many decimal places as there are in the number with the least decimal places. Hence, the total mass of the box is 2.3 kg.

Difference in masses = 20.17 – 20.15 = 0.02 g

In subtraction, the final result should retain as many decimal places as there are in the number with the least decimal places.