A teacher makes a saturated solution of potassium chlorate in 100g of 50°C water. The water cools down to 20°C. How much potassium chlorate precipitates out of the solution?
We don't know. Possibly NONE of the potassium chlorate precipitates.
The teacher made a saturated solution. AS specified, the amount of potassium chlorate in solution is equal to the amount of solute that would be in equilibrium with undissolved solute.
Now, we would expect that as the solution cools the solute would precipitate from solution, inasmuch as a hot solution can (generally) solvate more solute than a cold one. Nevertheless, even if solubility data were available, still no potassium chlorate might precipitate in that supersaturated solutions are possible, in which, by definition, the solution contains more solute than would be be in equilibrium with undissolved solute.
And so the question was not well proposed.