Results 1 to 2 of 2

Math Help - probability qn(not too hard!!)

  1. #1
    Member
    Joined
    Apr 2008
    Posts
    132

    probability qn(not too hard!!)

    A secretary receives application forms for a current vacancy and has to check them for completeness before further processing is carried out on them. About one in every 20 is incomplete.
    i) What is the probability that at least one incomplete form will occur in two successive forms that the secretary checks?
    ii) In a batch of 100, what is the probability that at least one incomplete form will occur?
    iii) How many form checks would result in a 10% chance of coming across an incomplete form?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by matty888 View Post
    A secretary receives application forms for a current vacancy and has to check them for completeness before further processing is carried out on them. About one in every 20 is incomplete.
    i) What is the probability that at least one incomplete form will occur in two successive forms that the secretary checks?
    ii) In a batch of 100, what is the probability that at least one incomplete form will occur?
    iii) How many form checks would result in a 10% chance of coming across an incomplete form?
    i) \left( \frac{1}{20} \right) \left( \frac{1}{20} \right) + \left( \frac{1}{20} \right) \left( \frac{19}{20} \right) + \left( \frac{19}{20} \right) \left( \frac{1}{20} \right)


    ii) 1 - Pr(none)  = 1 - \left( \frac{1}{20} \right)^{100}.


    iii) Let x be the random variable number of incomplete forms.

    X ~ Binomial( p = 1/20, n = n).

    You require Pr(X > 0) > 0.1 => 1 - Pr(X = 0) > 0.1 => Pr(X = 0) > 0.9.

    So solve \, \left( \frac{19}{20} \right)^n > 0.9 \, for the smallest integer value of n. I get n = 3.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Hard Probability Question
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: August 3rd 2010, 08:15 AM
  2. Hard Probability
    Posted in the Statistics Forum
    Replies: 6
    Last Post: May 31st 2010, 12:40 PM
  3. hard probability question
    Posted in the Statistics Forum
    Replies: 5
    Last Post: June 14th 2009, 04:51 AM
  4. omg probability is so hard!! =[[
    Posted in the Statistics Forum
    Replies: 2
    Last Post: April 16th 2009, 08:30 PM
  5. Hard probability
    Posted in the Statistics Forum
    Replies: 0
    Last Post: October 15th 2007, 12:32 AM

Search Tags


/mathhelpforum @mathhelpforum