00:01
Okay, here we have the standard normal curve, which looks like this, the z curve.
00:10
You have symmetry about the y -axis, so the mean is zero, standard deviation is one.
00:18
Now the area under the curve is always one.
00:21
So is the chance of lying between c and this number here is 0 .2246.
00:28
That means the area between c and minus .67 has to be at the number they give you .2246.
00:43
Knowing that, i want to work out somehow the value of c.
00:47
Well, the first step is find the area below minus .67.
00:51
In other words, i want to work out this area in green first.
01:01
To do that, so let's say then the green area, i will use a function called normal cdf on the ti84 class calculator.
01:16
So normal cdf, and to get that, what you do, you press second, so the blue button, so second followed by var's vars, just below the arrow keys on the right.
01:31
That brings up the menu for distributions.
01:35
And you'll find normal cdf number two on the list.
01:39
So with the arrow key, choose that, and press enter.
01:43
And the input is lower, upper, mean, style, deviation.
01:48
The lower one is done for you.
01:50
Negative 1e99.
01:52
That is some number, of course, it's way over here on the left.
01:56
If you want to put minus 10 there, that's fine too.
01:59
We'll change the answer.
02:00
To some number far away on the left.
02:06
So i'll put here negative 100.
02:10
Upper is minus 0 .67.
02:14
Mean is 0.
02:16
It's mu and style of deviation is 1.
02:20
Place that in.
02:22
Check the numbers.
02:24
And you should get, one second here.
02:27
I put in negative 100 for lower, negative 0 .67 for upper, 0 .1...