used. Duncker also pointed out that the phenomenon occurs not only with physical objects, but also with mental objects or concepts (a point which lends itself nicely to the phenomenon of Einstellung effect). Luchins and Luchins water jar experiment The water jar test, first described in Abraham S. Luchins' 1942 classic experiment, is a commonly cited example of an Einstellung situation. The experiment's participants were given the following problem: you have 3 water jars, each with the capacity to hold a different, fixed amount of water; figure out how to measure a certain amount of water using these jars. It was found that subjects used methods that they had used previously to find the solution even though there were quicker and more efficient methods available. The experiment shines light on how mental sets can hinder the solving of novel problems. In Luchins' experiment, subjects were divided into two groups. The experimental group was given five practice problems, followed by four critical test problems. The control group did not have the five practice problems. All of the practice problems and some of the critical problems had only one solution, which was "B minus A minus 2·C." For example, one is given Jar A capable of holding 21 units of water, B capable of holding 127, and C capable of holding 3. If an amount of 100 units must be measured out, the solution is to fill up Jar B and pour out enough water to fill A once and C twice. One of the critical problems was called the extinction problem. The extinction problem was a problem that could not be solved using the previous solution B − A − 2C. In order to answer the extinction problem correctly, one had to solve the problem directly and generate a novel solution. An incorrect solution to the extinction problem indicated the presence of the Einstellung effect. The problems after the extinction problem again had two possible solutions. These post-extinction problems helped determine the recovery of the subjects from the Einstellung effect. The critical problems could be solved using this solution (B − A − 2C) or a shorter solution (A − C or A + C). For example, subjects were instructed to get 18 units of water from jars with capacities 15, 39, and 3. Despite the presence of a simpler solution (A + C), subjects in the experimental group tended to