Question

In a class of 6, there are 4 students who are secretly robots. If the teacher chooses 2 students, what is the probability that neither of them are secretly robots?i know how to get 2/6 but how do i get the other fraction?

Answer 1

The chance of the first student chosen not secretly being a robot is 2/6, but if the student is secretly a robot, then it doesn’t matter who the second student chosen is, because “neither” cannot be obtained.

So, 2/6th the time we care about the second student. There is in this case 1 non robot among the 5 remaining students, so the chance is 1/5 of picking that second non robot.

Hence;

2/6 x 1/5 = 2/30 = 1/15