00:01
Okay, we are told the diameter of a ball bearing is, or follows rather, a normal distribution with the mean of 22 millimeters in the center, as here, as always.
00:16
And the standard deviation of 0 .016 millimeters, that's here.
00:22
Now, we need to have between 21 .97.
00:26
So let's say that's here, 21 .97 and 22 .03 to be acceptable.
00:40
The area under a normal curve is always one.
00:43
So if i find this area here, that's my answer.
00:47
That's the chance the diameter is going to be accepted.
00:56
So i want to work out that red area.
00:58
And to find that, the ti -84 plus use the function called normal cdf.
01:08
And to find that, you press second to the blue button, followed by vars, v -a -r -s, on the right, just below the arrow keys.
01:19
That brings up the menu for distributions, and item 2 is normal cdf, so choose out with the arrow key and press enter.
01:27
It's a four number input and the first one is 21 .97.
01:35
That's the lower, the upper 22 .03, the mean 22 and deviation 0 .16.
01:46
That's the input to work out the area in red.
01:51
So what we have then, lower 21 .97, upper 22 .03, the mean 22 .03, the mean 22.
02:02
And 0 .016 for the time deviation.
02:10
And that becomes 0 .932.
02:14
And what i want is percentage.
02:18
So it's 93 .92 % chance.
02:23
And i want nearest 10.
02:26
So 93 .9 % is the answer.
02:35
Okay.
02:36
Now part b.
02:37
Let's the range if i want to accept 98 % of the ball bearings.
02:46
Okay, install a new diagram then, like this.
02:56
Means still 22, sign deviation, 0 .016.
03:02
What i want to do is work out, it's called x1 and x2, where this area here is going to be 98%...