00:02
In this problem, we will determine the standard deviation for a certain random variable.
00:07
Now in this problem, an water dealer hands out 1 ,000 lottery tickets and there is a price for a new car which is worth $25 ,000.
00:16
Now what we need to find is the standard deviation for the amount one for someone with a single ticket.
00:23
Now in order to determine this, first of all, we need to find the mean.
00:27
Now the mean is equals to the expected value of the random variable and that is equals to summation x times px where x is the payoff and px is the probability of that payoff.
00:46
Now the first payoff is zero for a ticket which is not the winning ticket.
00:53
If there is any ticket which is not the winning ticket, then the payoff will be zero.
00:57
And this will be multiplied with the probability of getting a ticket which is not the winning ticket.
01:02
Now there are a total of 1 ,000 lottery tickets.
01:06
So there will be 99 lottery tickets which are not the winning tickets.
01:13
Since there is only one winning ticket, 99 out of the 1 ,000 lottery tickets are not winning tickets.
01:19
So the probability of getting a payoff of 0 will be 99, divided by 1 ,000.
01:27
Now because of the summation we add with this the next value of x and px...