# Math Help - probability

1. ## probability

i. At the local school, seven boys and eight girls have nominated for prefect. If three boys and three girls are selected, in how many ways can this be done.

ii. At their first meeting the six prefects sit around a circular table. What is the probability that the two captains do not sit together?

2. Originally Posted by deej813
i. At the local school, seven boys and eight girls have nominated for prefect. If three boys and three girls are selected, in how many ways can this be done.

ii. At their first meeting the six prefects sit around a circular table. What is the probability that the two captains do not sit together?
i. ${7 \choose 3} \cdot {8 \choose 3} = \, ....$

ii. Pr(captains don't sit together) = 1 - Pr(captains do sit together) and Pr(Captains do sit together) = (2!)(4!)/5!

3. ok so is the answer to i. 5644800
and i still dont get ii.

4. Originally Posted by deej813
ok so is the answer to i. 5644800
and i still dont get ii.
Start by reviewing your notes on re-arrangements in a circle.

5. ok so i just read some examples and am now totally confused
obviously the answer i said is way too big
so how does it work