00:01
Okay, we have here then a normal distribution, or the words, the usual bell -shaped curve.
00:06
Along here is time taken to complete the exam.
00:11
And it looks like that.
00:13
The mean here in the middle is 77, and we're told the standard deviation is 12.
00:21
I want to work out a chance that a student can complete the exam in less than one hour.
00:29
Okay, so one hour then, 60 minutes.
00:33
That will go here somewhere.
00:35
I want to work out a chance the student is that area there.
00:41
The key thing here is the area under a normal curve is always one.
00:45
So find that red area, and that's the answer.
00:49
Or to find it, use a calculator.
00:51
The ti -84 plus is a good one to use.
00:56
And the function you need is called normal cdf.
01:01
That you will find by pressing second, followed by vars, v -a -r -s, on the right, just below the arrow keys.
01:09
That brings up the menu for distributions.
01:12
Number two on the list is normal cdf.
01:15
Press that.
01:16
Lower is some number way over here on the left, or put in zero, actually, it'll be fine.
01:24
So, zero will work.
01:26
Upper is 60.
01:27
Mean 77 via deviation 12 and that i work out so 060 77 and 12 paste that press enter and we get 0 .078 29 and what they want here is in fact four decimal places so the answer is 0 .078 3 so a small chance.
02:07
Okay, part b, what i want is above 60 and below 75...