00:01
So in this question we're told that we have a lottery where we pick four numbers without replacement from the numbers 1 to 50, and we win if our numbers match four drawn numbers, and order is not important.
00:40
So first of all, how many samples of size 4 are possible from a population of n equals 50? so the number of samples is just 50 choose 4, which we can also write as 50 choose 4 in this way.
00:59
So 50 choose 4 is equal to 230 ,300.
01:08
So that's the number of possible samples.
01:12
Part b, let's say that we choose the numbers 10, 20, 30, and 40.
01:23
What's the probability of winning the grand prize? well, the probability of winning is the probability that that sample is chosen.
01:32
So it's the number of winning samples divided by the number of samples that are possible.
01:41
But there's only one sample that wins because you've only got one group of numbers.
01:46
And we already know how many winning samples there are.
01:49
There's 230 ,300.
01:51
So that's your probability of winning.
01:56
So what's the probability of not winning? well, that's just 1 minus the probability of winning.
02:05
So we have 1 minus 1 over 230 ,300.
02:12
Well, that's just going to be 230 ,299 over 230 ,300.
02:25
Now part d, let's say, so how many combinations are there available that include 20, 30, and 40, but not 10? so what's the number of samples including 20, 30, 40, but not 10? well, what we're going to do is we're going to say we have four numbers drawn in a row.
02:55
Three of them are 20, 30, and 40.
02:59
And the other one is any other number that isn't 10.
03:04
So we've got to pick, first of all, which ball is going to be the one that isn't 10, 20, 30, or 40.
03:13
And there are four places that the one that's not 20, 30, 40, or 10 can be placed.
03:24
So this is the places we can put our not 20, 30, 40, or 10...