00:01
So i've set up the probability distribution in a table for the number of accidents 0 through 6 and the probability of those happening.
00:07
To find the mean, you just times each one of these and add.
00:11
So 0 times 0 .29 is 0, plus 1 times 0 .34 is 0 .34, plus 2 times 0 .15 is 0 .30, plus 3 times 0 .08 is 0 .24, plus 4 times 0 .07 is 0 .28, plus 5 times 0 .05 is 0 .25 plus 6 times 0 .02 is 0 .12.
00:47
So when you add those up, the mean equals 1 .53.
00:53
That's the expected value on that table, 1 .53.
00:57
The standard deviation is a really long formula.
01:01
Usually you can do this on a calculator.
01:04
What you do is you take each value in the table, 0 minus the mean 1 .53 and then you square that difference and then you multiply it by the probability of that 0 happening so rather than write out all six of these and i'm adding so i would dot dot dot all the way and i would would finish with 6 minus 1 .53 squared times 0 .02...