Simple Math Question

[RedAlert]

Hey guys,

 

This is just a grade 10 level math question that I have, that will be extremely simple for you, but I am unable to understand what to do (I am in Grade 10 too).

 

The problem is that there are 9 people playing sports, and they need to divide up into teams of 2. How many different ways can they form their groups?

 

The answer for this question is 20, but how do you get that answer? I am totally confused, and all your help in clarifying this matter is greatly appreciated.

 

Thanks,

RedAlert

[ed84c]

Hmmm try doing 2nCr10 on your calculator or 10nCr2 i can never remember which way round it is.

[RedAlert]

What is nCr? We have not learn that yet. If possible, could you please explain the concept?

[matt grime]

The answer can't be 20.

 

Any way of pairing these people up must leave one person out on their own. Their are 9 different ways to pick one person to leave out, and so the answer must be divisible by 9.

 

Anyway, counting now, we can leave out1 person in nine ways, and you need to figure out how many ways to split 8 people into pairs. Just do it with a pen and paper. Perhaps try doing it for 4 people, first, then 6 poeple, try to spot a pattern.

[The Thing]

9C2.

Either that or 9P2. I can't remember which.

Look on your calculator for the buttons nCr or nPr. They're usually 2ndFunctions, and a good scientific calculator will have them.

And google permutations and combinations.