Explanation:
1. I estimate that the error in measuring the area of the lot is about 10% so we write the area as 400 sq ft +- 10%, which means that the lot can be as small as 360 sq ft or as large as 440 sq ft. We tack on 15% more on the number of pieces of sod to account of the plot's irregularities. Since each piece of sod is 2 sq ft, the number of pieces we must get is 440/2 = 220 pieces +- 15% or 253 pieces
2. The nominal value is jus the average weight which is 59.5 g. The tolerance is (3.5g/59.5g)×100% = 5.88% and the measurement range is from 56g to 63g.