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**1. Homework Statement**

1/ A committee of 6 is selected from 10 people, of whom A and B are two. How many committees can be form excluding A if B is included ?

2/ A committee of 5 is to be chosen from 6 boys and 4 girls. How many committees can be form containing a particular boy X but excludes a particular girl Y?

3/ In a box there are 4 black counters and 5 white counters. 4 counters are withdrawn one at a time. (the first counter being replaced before the second counter is drawn). Find the probability that two black counters and two white counters are drawn, in any order.

2. Homework Equations :

Premutation and Combination

2. Homework Equations :

Premutation and Combination

**3. The Attempt at a Solution**

1/ I do this two way.

1st: 8C5 (no B but A) + 8C5 (no A but B) + 8C6 (no B no A) = 140

2st: 10C6 - 8C4 (A and B included) = 140

*I have no question for this one. However, the question comes when i do n.o 2*2/ I do the same thing because it looks very similar to the question n.o 1. I made 10C5 - 8C3. However the answer is 8C4 :|. And of course the answers are not the same number form the calculator. Please check for me :(

3/ I do (4C2 x 5C2) / 9C4. And i know the answer is not correct as the book :(

Please help me :( The exam is coming !!