How do you separate ragi and mustard by threshing?

Answer 1

You usually use a physical property that is different between two materials to separate them out of a mixture.

One such difference is that salt dissolves in water while mustard seeds don't, so if you place the mixture in water and dissolve the salt, then filter out the salty water (with, say, a coffee filter), you will be left with just the mustard seeds from the mixture.