00:02
To answer these questions about todd and his scores, we're going to be calculating a z score for each class, which we can find the z score by doing the observed value minus the mean divided by the standard deviation.
00:15
So in bio, todd's z score is going to be his score, 82, minus the mean, 65 .8, divided by 8 .15 as the standard deviation.
00:28
And that tells us his z score in bio is 1 .99.
00:36
And we want to know what percentage of his class scored higher than him.
00:41
So we're going to need the standard normal probability table, and we're going to look up a z score of 1 .99.
00:48
And when we do that, it tells us the area to the left, or the probability to the left of his z score, is 0 .9767.
00:55
So he scored higher than 97 .67 % of the students.
01:01
But we want what percent scored higher than him? so we're going to do 1 minus .9767, which comes out to be 0 .031, or 2 .31 % of the students scored higher than him.
01:19
Next, we'll do polly -sai the same way...