00:01
Okay, here we have 12 students in the class and there are three different tests.
00:05
Let's call them a, test a, test b and test c.
00:10
There are my three tests.
00:12
And four students take each test.
00:16
So three tests, four times three, twelve.
00:19
So test a, for example, there are going to be 12, c, four ways to choose the four people who take that particular test.
00:34
12 in total, and i want four of them.
00:37
So in 12 c4, i can work out.
00:40
That will be 12 factorial, over 8 factorial, 4 factorial.
00:46
And that i can work out manually or even easier.
00:50
The ti 84 plus, press the math button on the left.
00:54
With the arrow key, go across to prob, go down to ncr, and just type in 12.
01:03
C4, and that is 495.
01:09
So, test a then, 495 ways, picking four students...