Pulsified333 one year ago Suppose that you flip a coin 13 times. What is the probability that you achieve at least 5 tails?

1. anonymous

thats a binomial probability problem

2. anonymous

lol your math teacher must hate you

3. anonymous

lol

4. anonymous

at least 5 means 5 or 6 or 7 or 8 or 9 or 10 or 11, or 12,or 13

5. Pulsified333

No he just gives us insane amounts of homework while the other teachers at the university give like half of what he gives us

6. anonymous

you can compute the probability you get 0,1,2,3,4 and subtract that total from 1 it is still going to be a pain

7. anonymous

$P(x=0)=\left(\frac{1}{2}\right)^{13}$

8. anonymous

naw chill just use the formula of sumation

9. anonymous

10. anonymous

$P(x=1)=13\left(\frac{1}{2}\right)^{13}$

11. anonymous

use you calculator to plug it into a summation

12. Pulsified333

haven't learned that formula yet

13. anonymous

:(

14. anonymous

$P(x=2)=\binom{13}{2}\left(\frac{1}{2}\right)^{13}$

15. anonymous

ok how about the nCr * p^r * q^(n-r) ?

16. Pulsified333

yeah i know that

17. anonymous

ok now plug it in for the values 1, 2, 3, 4, 5 and add them then subtract that sum from 1

18. anonymous

1, 2, 3, 4, 5 being your success rate

19. anonymous

cool?

20. Pulsified333

yeah

21. Pulsified333

but what does (13 2) mean?

22. anonymous

13 tries and there are only 2 possible outcomes

23. Pulsified333

oh okay

24. anonymous

subtract this number from 1 http://www.wolframalpha.com/input/?i=%281%2B13%2B78%2B286+%2B715%29%2F2^%2813%29

25. anonymous

lol

26. Pulsified333

thanks :D