Solution :
It is given that a psychologist wants to determine the difficulty of the task influences on the estimate of how long people spend working on it.
Now we have to describe a experiment by using a completely randomized design and learn the effect of the difficulty on the estimated time is by randomly assigning 15 students to a Group 1 of easy mazes and other 15 students to the second group 2 of hard mazes. And then we compare the time estimates of the two groups.