Jayanthy can separate out the 3 substances by using a combination of 2 properties: water solubility and density. Salt is soluble in water, sawdust and gravel are not. Sawdust is lighter than water, while gravel is heavier. Here are the steps to separate out everything.
- Dissolve the mixture in water using a teaspoon or a spatula.
- Sawdust, being lighter (specific gravity < 1) will float on top of water and can be removed or skimmed off by using a spoon or spatula. Dry it at room temperature or out in the Sun.
- Filter the water through a piece of filter paper or cloth to separate the dust out. Dry out the gravel in sunlight or in an oven.
- Leftover water contains salt in it. Heat the solution to evaporation and obtain the salt.
Hope this helps.