probability

[markosheehan]

a subcommittee of three people is to be chosen from a committee of 10.
(i)how many subcommittees are possible?
(ii)how many subcommittees are possible if two particular people on the committee refuse to work together on the subcommittee?
(iii)if the subcommittee is chosen at random what is the probability that the two people who refuse to work together will both end up on the same subcommittee

i can work out the first question it is 10nCr3 which gives a answer of 120 but i cant work out the rest of the question

[ydoaPs]

!

Moderator Note

What do you have so far? How do you think you should go about it? We're more than happy to give homework help, but we don't give homework answers. Is there anything about the problem specifically that you don't understand?

[TakenItSeriously]

i) hint: do a search for the combin function to find your solution

ii) hint: how many different groups can you and your enemy create and how does knowing this help you find your answer.

ii) hint: for finding the probability, you are looking for the ratio of a smaller group within the total number of all possible groups.

You need to figure out what group they are talking about and figure out its size.