Answer:
8/27
Explanation:
First, we figure out how many students chose each school activity, so that we can find the probability of a student at random choosing running by putting (total running students)/(all students).
39 students chose tennis, as stated in the problem.
37 students chose football, as stated in the problem.
The total number of students who chose running must therefore be the the students who chose tennis and football, subtracted from the total number of students. 108 - 39 - 37 = 32, so 32 students chose running.
Therefore, the probability that a student at random chose running would be 32/108 or 8/27.