00:01
Okay, we have here 12 students, 7 female, 5 male, and the first part, i choose a committee of 3 from the 12 people, and it's no restrictions.
00:14
So it's 12 to choose from, so 12 choose 3.
00:19
And 12c3, you can work out one of two ways, either manually it's 12 factorial, over 9 factorial, 3 factorial.
00:28
That's from the ncr formula.
00:32
Or go to the ti84 plus, press the math button just below the alpha key.
00:38
And then with the arrow key, select the rob, the fourth one on the right, and go down to ncr.
00:46
And just type in 12 , and get the answer of 220.
00:54
That's the first one.
00:58
Now, part b says there must be exactly two girls.
01:06
So that means we have two girls and one boy.
01:19
Now, i can choose the girls.
01:23
I want two of them.
01:25
I have seven to choose from, seven female students.
01:28
Seven choose two.
01:30
For one boy, there are five boys, choose one.
01:36
So again, i can work out 7c2, either a 7 factorial over 5 factorial or 2 factorial.
01:46
And then i can work it out pretty quickly.
01:48
I divide up by that, i get 7 by 6 remaining, divide by 2, so 21...