In a class of 40 students, 25% scored an A on a test, 35% scored a B, and the rest scored a C. If a student is chosen at random from this class, what is the probability that they did not score an A or a B?
Let's first find out how many students scored an A or a B:

1. The number of students who scored an A is 25% of 40, which is 0.25 * 40 = 10 students.
2. The number of students who scored a B is 35% of 40, which is 0.35 * 40 = 14 students.

Now we know that there are 10 + 14 = 24 students who scored either an A or a B. Since there are 40 students in total, the remaining students must have scored a C:

Number of students who scored a C = 40 - 24 = 16

The probability of choosing a student who did not score an A or a B (i.e., scored a C) is:

Probability = Number of students who scored a C / Total number of students
Probability = 16 / 40
Probability = 0.4

So, the probability that a randomly chosen student did not score an A or a B is 0.4.