## Safari321 3 years ago Six students are pairing up to play tennis.In how many different ways can they pair up?

1. mridrik

This is not permutations luis, it's combinations

2. Safari321

720 ways?

3. mridrik

he is wrong

4. Safari321

oh

5. mridrik

he was saying that if Anne and Bill paired up, it would be different than Bill and Anne pairing up

6. Safari321

oh

7. mridrik

it can be written as nCr which means n choose r, where n is larger. so in this case it is 6 choose 2, and to find the answer, you plug them into this formula: |dw:1331001470884:dw|

8. satellite73

pick one person, person A then their are 5 choices for partners. after that pick another, there are 3 choices of partners. then no choices

9. Safari321

so there's a formula for combinations?

10. mridrik

! means factorial, and you multiply by all the natural numbers less than the number in front of the !, so for 6! it would be, 6 x 5 x 4 x 3 x 2 x 1

11. Safari321

then that'll be the outcome of the of combinations?

12. mridrik

6! = 720, then we divide by 2! (which is just 2) times (6-2)! 2 x 4! = 4 x 3 x 2 x 2 x 1 = 48, so the answer is 720 divided by 48 which simplifies to 15

13. Safari321

okay mridrick thanks!

14. mridrik

you're welcome

15. Safari321

:)

16. mridrik

:D