There are 8 floors in a building excluding ground floor. 4 people get in the lift along with Mr X on ground floor. Given that each person get off the lift on a different floor, what is the probability that Mr X gets off the lift before exactly 3 people?

Not clear with the explanation for the 5th question, can you please explain a bit further? I can solve it by the traditional method but would like to explore more of this symmetry thing for knowledge,hence asking.

Probability of 3 heads = Probability of 3 tails (which is 2 heads).
Probability of 4 heads = Probability of 4 tails (which is 1 head).
Probability of 5 heads = Probability of 5 tails (which is 0 heads).

There are 8 floors in a building excluding ground floor. 4 people get in the lift along with Mr X on ground floor. Given that each person get off the lift on a different floor, what is the probability that Mr X gets off the lift before exactly 3 people?

Diana, that is one of the questions I had included in today’s post ðŸ™‚ Check it out…in a couple of hours…

regards

J

Not clear with the explanation for the 5th question, can you please explain a bit further? I can solve it by the traditional method but would like to explore more of this symmetry thing for knowledge,hence asking.

Probability of 3 heads = Probability of 3 tails (which is 2 heads).

Probability of 4 heads = Probability of 4 tails (which is 1 head).

Probability of 5 heads = Probability of 5 tails (which is 0 heads).

Now think ðŸ™‚

regards

J