00:01
We have been given a discrete probability distribution, and we want the mean, variance, and standard deviation.
00:08
Let's start the mean.
00:09
To find the mean of a probability distribution, you take each value of x, you multiply by the probability, you add them up.
00:17
A lot like finding the mean of a frequency table, except we don't have to divide by n, because probability is summed to one anyway.
00:25
So minus 42 times 0 .36 plus minus 27 times 0 .31 plus minus 15 times 0 .24 plus minus 6 times 0 .09.
00:42
So since this is the average, and it's all negative values, the average is going to be negative as well.
00:49
And it is minus 27 .63.
00:54
Now on to the variance.
00:56
So variance and since standard deviation are measures of spread, so they can never be negative.
01:03
To calculate variance, you take your value of x, you subtract the mean, mu, square the difference, multiply by probability, add them up.
01:14
Again, a lot like a frequency table...