The size analysis was carried out on a sample of gravel. The data for mass fraction and average particle diameter of the fraction is given in the following table: pi (mm 0.3 5 0.6 10 0.8 15 0.9 20 The...

Extracted text: The size analysis was carried out on a sample of gravel. The data for mass fraction and average particle diameter of the fraction is given in the following table: pi (mm 0.3 5 0.6 10 0.8 15 0.9 20 The volume surface mean diameter, D:of the sample -(mm) a) 2.34 mm b) 7.23 mm c) 4.59 mm d) 2.56 mm