First, we note that the 1500 white blood cells would form a row that is 2.54 cm long and figure out how many micrometers that is. 1 cm = 10,000 micrometers so 2.54 cm = 25,400 micrometers. Next we divide that by the 1500 white blood cells to find out how long each one is. 25,400/1,500 = 16.93 micrometers each. That is the length, or diameter, of each white blood cell.
