Results 1 to 3 of 3

Math Help - Probabilty problem

  1. #1
    Newbie
    Joined
    Oct 2010
    Posts
    2

    Probabilty problem

    Hello forum :]

    I am in need of some help on this probability problem.

    The probability of being born on a Friday the 13th is 1/214. Assume the days of people's birth are independent of each other.

    (a) You meet two new friends; what is the probability that both new friends were born on a Friday the 13th?

    I got this one, just use the multiplication rule so: (1/214)(1/214) = 1/45796

    (b) You meet 31 new friends; what is the probability that at least one of these new friends was born on a Friday the 13th?

    I cant figure this out. If they were disjoint then I could just use the addition rule, but they aren't so I am very confused.

    Any help will be greatly appreciated.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,682
    Thanks
    614
    Hello, Phodot!

    The probability of being born on a Friday the 13th is 1/214.
    Assume the days of people's birth are independent of each other.

    (a) You meet two new friends. What is the probability that
    both new friends were born on a Friday the 13th?

    I got this one, just use the multiplication rule so: (\frac{1}{214})(\frac{1}{214}) \:=\: \frac{1}{45,\!796} . Right!

    (b) You meet 31 new friends; what is the probability that
    at least one of these new friends was born on a Friday the 13th?

    The opposite of "at least one" is "none."

    The probability that none were borh on Friday the 13th is: . (\frac{213}{214})^{31}


    Therefore: . P(\text{at least one Friday the 13th}) \;=\;1 - \left(\frac{213}{214}\right)^{31} \;\approx\;13.5\%
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2010
    Posts
    2
    Thank you very much :]
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. problem involving probabilty
    Posted in the Statistics Forum
    Replies: 1
    Last Post: January 18th 2010, 11:11 AM
  2. Probabilty for a fair game problem w. binomials
    Posted in the Statistics Forum
    Replies: 6
    Last Post: November 22nd 2009, 12:23 PM
  3. Probabilty problem
    Posted in the Advanced Statistics Forum
    Replies: 8
    Last Post: May 19th 2009, 12:26 AM
  4. Probabilty problem
    Posted in the Statistics Forum
    Replies: 0
    Last Post: May 15th 2009, 07:09 PM
  5. NCAA Probabilty Problem: HELP!!!!!!!
    Posted in the Advanced Statistics Forum
    Replies: 8
    Last Post: March 28th 2008, 11:54 AM

Search Tags


/mathhelpforum @mathhelpforum