# Homework Help: Conditional probability

1. Nov 14, 2007

1. The problem statement, all variables and given/known data

The probability of a monitor not working is 0.005, the probability of a cpu faulty is 0.002, the probability of a keyboard damaged is 0.0025, what is the probability of the computer switching on? If you are then told that the conditional probability of the monitor not working given that the keyboard has been damaged is 0.05, how does this affect the answer?

2. Relevant equations
probability of monitor not working = 0.005
probability of cpu faulty = 0.002
probability of keyboard damaged = 0.0025

3. The attempt at a solution
For the first part is was solved ok with a venn diagram removing from 1 the summed up individual probabilities and the intersect probabilities giving 0.009472475, however for the second part I attempted adding P(M|K) to to each occurence of p(K) in(where P(k) is probability of the keyboard being damaged) the general equation obtained from the venn diagram, but my answer was off the mark of 0.0936025

2. Nov 15, 2007

### HallsofIvy

What exactly is meant by "the computer switching on"? That none of those malfunctions happens? 0.009472475 is the probability of at least one of those malfunctions happening and I have trouble reconciling that with "the computer switching on"!

Last edited by a moderator: Nov 15, 2007
3. Nov 15, 2007