Give reason why sand and saw dust cannot be separated by handpicking

1. Handpicking method is a process in which we separate a solid-solid mixture with the help of hand, considering that there is enough difference in size and color of the particles and our visible to our naked eyes.
2. For handpicking method the particles should be considerably large in size whereas sand and sawdust particles are too small in size to differentiate that's why we don't use handpicking method for the same.