00:01
In this exercise, we have eight independent computers, each of which fails on a given day with probability 0 .005.
00:10
So we have the probability of failure, and this is for each computer.
00:22
At the end of the day, any computers which have failed are repaired in the evening, so that the start of each day is a brand new day with all computers working.
00:33
That means that this rate of failure remains constant from day to day.
00:38
For part a, we are asked what is the probability that all eight computers fail in a given day? let's call this probability p.
00:52
Since the computers are independent from one another, it is going to be the probability of failure for one computer to the exponent 8.
01:08
And this comes out to 3 .906 times 10 to the minus 19.
01:15
For part b, we are asked what is the mean number of days until a specific computer fails? so let's define x as the number of days until a specific computer fails.
01:42
On each day, the probability is 0 .005.
01:46
So that remains constant from day to day, and each day is independent of the previous or future days...