00:01
So in question 73, we're looking at a question where it says, suppose the duration of a particular type of criminal trial is known to have a mean of 21 days and a standard deviation of seven days.
00:11
And that's just for one trial.
00:12
We're going to look at nine trials.
00:15
Part a says to define what the sum of x is.
00:19
So we're going to let the sum of x be the sum of the duration of nine trials and days.
00:34
It's just defining the value sum of x.
00:37
And b, it says we want to know what type of distribution we're dealing with and the mean is standard deviation.
00:44
So the sum of x is going to be a normal distribution in this case.
00:49
And we want to figure out the mean.
00:50
So mean of nine trials, we'll just put 9t here, is literally the mean of the mean of the next, plus the mean of the next nine times.
01:03
So essentially that's nine times the mean, which is nine times 21.
01:09
Nine times 21 is 189.
01:12
So that is our mean to find that up here.
01:16
Our standard deviation, standard deviation is pretty similar.
01:20
Standard deviation, nine trials.
01:21
Think about this.
01:22
This is essentially standard deviation in the first one, standard deviation in the second one, standard deviation the third one, so on and so forth.
01:28
However, we cannot add or subtract standard deviation.
01:30
So the trick here is to find the variance by square in every single one these guys.
01:36
So our variance of nine trials is all of these sevens squared and we're add together a total of nine of them...