00:01
So we have a normal distribution with a mean of 21 days and a standard deviation of 7.
00:06
And our question is, for the first one, what does x, our random variable, stand for? and it's going to be the duration of the trial, or the number of days that a trial lasts.
00:16
And so that x would be normal with a mean of 21.
00:22
And then depending on the way it's set up, you either would have 7 here if you're using sigma.
00:29
Some resources i've seen use the variance here.
00:34
So you're going to have to do what your textbook does.
00:38
Now, we want to find if you choose one, what's the probability that it lasts at least 24 days? so that's the likelihood of 24 minus 21 divided by 7.
00:51
And that is 3 7's.
00:52
And 3 divided by 7 is a value of approximately 0 .43.
00:57
And the area above 0 .43 is the same as that below negative 0 .43.
01:05
And that is 0 .3336.
01:11
And we also wanted a picture of that.
01:13
So here is our normal distribution with 21 in the middle.
01:18
And then we know if we come out one standard deviation, that would be at 28...