## anonymous one year ago Need Help! Its a combination problem.5

1. FireKat97

I don't think your factorial equation is right... follow this format $\frac{ n! }{ k! (n-k)! }$ and try simplifying now

2. anonymous

15! / 15! (5-15)!

3. anonymous

On my notes it says nCk = n!/(n-k)! k! so id rather do it that way :) but it would still be the same way right?

4. FireKat97

Wait actually

5. anonymous

I wrote the wrong number.. I just need to figure out how to simplify 15C5

6. anonymous

its supposed to be 3003 but idk how? I can do it from a calculator, but on a quiz i need to be able to show my work

7. FireKat97

You would get 15!/ 15!. -10! that way and I don't think you should have a negative factorial

8. anonymous

I got 15!/10! 5!

9. FireKat97

yup thats right

10. anonymous

|dw:1442908599294:dw|

11. anonymous

The way i simplified it was 15 14 13 12 11 10 _________________________ 10 5 4 3 2 1 I crossed out the 10's and then from there it doesnt seem right, but its the way my teacher taught us. so for ex, 5 *3 = 15 7*2 = 14

12. anonymous

so then 3 would go on top of the 15 and the 7 would go on top of the 14

13. FireKat97

yeah I did the same, then you can cancel a few other things out as well

14. FireKat97

yup seems right so far

15. anonymous

thats where im stuck because i cant get 3003 if i do then it would be 3 * 7 * 11 *13 but what happens to the 12?

16. FireKat97

17. anonymous

yes

18. FireKat97

okay so you have $\frac{ 15 . 14. 13. 12. 11 }{ 5. 4. 3. 2. 1}$

19. anonymous

yes

20. FireKat97

|dw:1442908920946:dw|

21. FireKat97

do you follow what I did there?

22. anonymous

is that a 4?

23. anonymous

above the 12?

24. FireKat97

yea

25. anonymous

okay yeah i understand so far

26. FireKat97

and it cancels with the 4 below

27. FireKat97

yup so now we have left 3 x 7 x 13 x 11

28. anonymous

OHH LOL OKAY I GET IT NOW ! AHHHH okay i was doing it right then

29. FireKat97

yup you were right all along ahahahha :D

30. anonymous

wait what happend to the 3? Lol

31. FireKat97

the bottom one got cancelled to make the 12 on top into a 4

32. anonymous

ooookay yay! thanks :)

33. FireKat97

haha no problem :)