00:01
In this exercise, we are told that the scores on a statistics exam, we'll call that random variable x, are approximately normally distributed with a mean of 70 .6, and standard deviation of 6 .46.
00:16
And we are asked to calculate the proportion of scores that are between 66 and 75.
00:23
So that is equal to the probability that x is between 66 and 75.
00:30
Now this can be re -expressed as the probability that x is less than or equal to 75 minus the probability that x is less than 66.
00:49
So that strategy is if our mean is 70 .6 and the distribution is approximately normally distributed, we have 75 here and 66 here.
01:12
We want to find the proportion that are in this area here.
01:17
So the strategy is to take the proportion or the probability that x is less than 75, which corresponds to all of this area to the left of 75, and then subtract from that the area to the left of 66.
01:47
And what that will leave is the area and the distribution that represents the probability between the probability that x is between 66 and 75.
02:05
And we can calculate these probabilities using excel.
02:08
So let's open up excel and we will use the norm .d .d.
02:15
Function to calculate this...