00:01
So we have the sheriff at dearborn collecting driving speeds on m39 and finds that they are normally distributed.
00:10
So therefore we could draw the bell shape curve.
00:13
The average is 78, so we can place the average at the center of our bell.
00:18
And our standard deviation is 14.
00:22
And he wants to address the speeds by focusing on ticketing the top 10%.
00:29
So our top 10 % would be this shaded area right here.
00:38
So we want to know what is the speed threshold that the sheriff has in mind for issuing those tickets.
00:47
So we want to find the speed.
00:50
So the most efficient way to find that is to start by finding the z score associated with that boundary line.
00:57
And we could find the z score by using inverse norm on a graph and calculation.
01:03
But when you use inverse norm, you have to provide the area in the left tail, followed by the mean and the standard deviation.
01:15
So for our scenario, we're going to use inverse norm, but the area in the left tail, what we have shaded is 10 % of the curve.
01:25
So to the left of that boundary line would be 90%.
01:29
So we're going to use 0 .90.
01:31
The mean of z scores is always 0, and our standard deviation.
01:36
Is one.
01:37
So we're going to arrive at the z score associated with this boundary line.
01:43
So i'm going to bring in my graphing calculator and to find inverse norm, you're going to hit the second button and the vers button on a texas instruments calculator...