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?

Answer 1

Answer:

total 6 and 4 are robots

Step-by-step explanation:

teacher chooses 2 at random

(Number of favourable outcomes) / (Total number of favourable outcomes)

4/6=2/3 for one outcome

The chance of the first student chosen not secretly being a robot is 2/6.

If the first student is secretly a robot 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.

2/6*1/5=2/30 which is also 1/15, or if you prefer 6.6666… %