00:01
In this question, we are looking at a normal distribution, so i will start by drawing it.
00:09
Total area under this curve is 1, or 100%, and it's symmetric.
00:14
So 50%, we'll get below the mean, 50 % above the mean.
00:19
So the mean mu is 580.
00:22
We're given the variance, s squared, is 72 .25.
00:28
I don't want the variance.
00:30
I want the standard deviation.
00:32
So i'm immediately going to square root this to get 8 .5.
00:39
What percentage will score below 70? so if i put 70 here, it's going to be below the mean, quite far below the mean, and we want to know what percentage score below.
00:53
So our next step is to find the z score.
00:55
Z is x minus mu over sigma.
00:59
It tells you how many standard deviations away from a mean a value is.
01:04
So here we have 70.
01:06
Minus 580 over 8 .5...