00:01
We are looking at a normal distribution.
00:03
I will start by drawing it.
00:05
The total area under this curve is 1, or 100%, and it is symmetric.
00:10
The mean is 0, the standard deviation is 1.
00:13
So this isn't just any normal curve, this is a standard normal curve, if it has these particular parameters.
00:23
Now we want to find the 81st percentile.
00:26
So that's defined as the point where 81 % of the curve is below it, 19 % above.
00:31
So that's going to be up here somewhere.
00:33
P 81.
00:35
So this area below is 0 .81.
00:41
This area is 0 .19.
00:46
Okay, so how do we find that? well, we have been given a table, the standard normal table, and this table gives you the area between a value and the mean.
00:59
So if you look in the table, unless it's a cumulative table, which is great, if it's cumulative, that's area to the left, just look for 0 .81 and you're done.
01:07
But it's probably a standard table so it won't have 0 .81 in it...