00:01
All right, so we're told that hour -long tv shows have, last an average of 43 minutes, 43 minutes, and a staring deviation of 1 .25 minutes without commercials.
00:21
And for this, we're going to assume that this is normally distributed, otherwise we wouldn't be able to do this.
00:31
But we can, so we want to know the probability or the proportion of the shows that are between 40 and 44 minutes.
00:39
So here's 40 and 44 minutes.
00:43
We want to know this.
00:47
So between that's what i want to do.
00:51
That's a picture.
00:52
So the way we do this is we find the area to the proportion less than 40.
00:57
And then we find the proportion that is less than 44.
01:04
And then what we do is we take the probability or the proportion of x being less than 44.
01:11
And we subtract the probability of x being less than 40 and voila we're left with everything we want all that stuff in the middle so let's do that so we need to get to these x's to z scores and you're going to use this transform here x minus mu over sigma and so we take our our mean which is 43 that goes in for mu here so minus 43 all over sigma which is one point 0 .25.
01:48
And when we put our x value in there, we will say we'll do 44 first.
01:54
That gives us a z score of 0 .78814.
01:59
We do a table lookup.
02:00
We find that value is 0 .77995.
02:05
0 .77995...