00:01
We have been told that 1 in 10 tickets wins a prize on a particular lottery.
00:05
We purchased 900 tickets, so probability of each of these winning will be 1 in 10, 0 .1.
00:12
We want the probability that the number of wins, so r squared x, is greater than 100.
00:19
So initially looking at this, i see a binomial distribution.
00:23
N independent trials, two outcomes, you win or you don't, same probability p for each ticket.
00:28
And i'm going to take a normal approximation to this binomial.
00:34
So we have a normal curve, the mean is np, the standard deviation root np1 minus p.
00:44
These are the mean and standard deviation of a binomial.
00:48
So the mean is 90, standard deviation 9.
00:52
900 times 0 .1 times 0 .9 is 81, and then square root it.
00:58
100 is above the mean, and we want greater than, area to the right.
01:02
But before we go ahead and solve this normal distribution question, we have one more step.
01:07
It is called continuity correction.
01:14
If we were to zoom in at this point on the binomial, we would have a series of rectangles.
01:19
A binomial is a discrete distribution...