00:01
Okay, we are told the time taken for the computer to boot up follows a normal distribution, which means it looks like this.
00:08
Here is time in seconds and the bell curve shape, as usual.
00:14
The mean is 30 seconds.
00:17
That goes in the middle.
00:19
We have symmetry about the mean.
00:21
Here is 30.
00:22
And we are told the sound deviation is 5 seconds.
00:26
I want to work out the chance that the computer will take more than 42 seconds.
00:33
So over here then is 42 seconds.
00:36
Now the area under a normal curve is 1.
00:39
So if i find this area here, that's the answer to the question.
00:44
So, p of time greater than 42 seconds equals the red area on my diagram.
00:56
And to find that, what i do is i use a calculator, the ti -84 plus, for example...