At my old alma mater there’s simple aptitude test to determine whether a candidate should pursue mathematics or engineering.
Each candidate is placed in a room in which there is a sink, a gas stove, a box of matches, and a kettle sitting on the floor. The problem given is to boil a kettle of water. The solution, of course, is to fill the kettle at the sink, place it on the stove, and light the stove with a match. Almost everyone solves this successfully.
In the second part of the test, each candidate is shown into the same room and given the same problem, but this time the kettle is filled with water and sitting on the stove.
The candidates with an aptitude for engineering strike a match and light the stove.
Those more suited to mathematics pour the water out of the kettle and set it on the floor. This reduces the problem to its previous case, which has already been solved.