00:01
We need to pick 12 sales representatives from a collection of 15, three in each of five regions.
00:08
We want the probability that the 12 representatives only come from four other regions, so one region is completely ignored.
00:16
So we're picking people, we have 15 in total, we are picking 12 of them from a group without replacement, and the order in which we pick them doesn't really matter.
00:26
So this is going to be based on combinations.
00:30
I'm going to start by finding how many ways we could pick people just in general.
00:35
So that's 15 choose 2.
00:39
And your calculator should have a button to do that for you.
00:42
Oh, sorry, 15 choose 12.
00:45
We're picking 12, which is 455.
00:51
So there are 455 ways to pick these representatives since it's chosen at random.
00:58
Then they're all equally likely to happen.
00:59
So each possible combination is one out of 455.
01:05
So how many combinations meet our criteria? if i put it on the numerator, i will have my answer...