To show the effect of particle-size distribution on the rate of extraction, consider an oil-containing solid containing some particles half the average size and some 15 times the average size (say 25 percent 0.5 mm, 50 percent 1.0 mm, and 25 percent 1.5 mm). For an effective diffusion coefficient of 1 X 10^-7 cm/s², determine the times for 50, 90, and 99 percent extraction and compare with the predicted times based on the average particle size.