Conditional probability

1. May 26, 2015

diracdelta

1. The problem statement, all variables and given/known data
Profesor has 17 keys, and only one unlocks the door.
Let random variable X be attempt at which profesor unlocks the door (key that doesnt work is saved by side)
Find:

a) Most probable value of variable X
b) In which attempt will profesor unlock the door
c) Probability that he will unlock the door between (X- σ) and (X + σ)

3. The attempt at a solution
a)
The most probable value is the x where p(x) is maximum.
How should i find it here? To find maximum i need some type of distribution.
b) This follows after i solve a)
c)also

2. May 26, 2015

Ray Vickson

PF rules require you to show some effort at solving the problem.

You need to determine the probabilities $P(X = 1), P(X = 2), \ldots$, etc. So, to say that the event $\{X =1\}$ occurs, what must happen when the professor selects keys? What is that event's probability? To say that the event $\{ X = 2\}$ occurs, what must happen when the professor selects keys? What would be the probability of that event?

Keep going like that.