+ Reply to Thread
Results 1 to 3 of 3

Thread: Probability question

  1. #1
    Points: 9, Level: 1
    Level completed: 17%, Points required for next Level: 41

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Probability question




    A teacher says 40% of students study for a specific test. If she randomly selects 5 students, whats the probability that 3 studends did not study for the test?

    So i tried to solve it like this but im not sure if its the right way. I assumed that since the problem is giving you a percentage we can say that out of 100 40 studied and 60 did not:
    (60C3)(40C2)/(100C5)
    Is this thw correct way to do it?

  2. #2
    Points: 5,044, Level: 45
    Level completed: 47%, Points required for next Level: 106

    Location
    Michigan, USA
    Posts
    24
    Thanks
    0
    Thanked 1 Time in 1 Post

    Re: Probability question

    This sounds to me like a binomial probability distribution problem. Your calculation is a hypergeometric equation. But you don't really know the finite quantity of the population. So, you could consider 40% as the success rate and 60% as the failure rate in a binomial problem. The probability that 3 students did not study means that 2 students did study out of the 5 students sampled.

    So, using the binomial formula: (5 C 2)*(0.4)^2 *(0.6)^3 = 0.346

    The probability is an approximation that is pretty good as long as the sample size is no more than 5% of the total population. Anyway, that's what I'm thinking. Hope this helps!

  3. #3
    Points: 9, Level: 1
    Level completed: 17%, Points required for next Level: 41

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Probability question


    Quote Originally Posted by spengel View Post
    This sounds to me like a binomial probability distribution problem. Your calculation is a hypergeometric equation. But you don't really know the finite quantity of the population. So, you could consider 40% as the success rate and 60% as the failure rate in a binomial problem. The probability that 3 students did not study means that 2 students did study out of the 5 students sampled.

    So, using the binomial formula: (5 C 2)*(0.4)^2 *(0.6)^3 = 0.346

    The probability is an approximation that is pretty good as long as the sample size is no more than 5% of the total population. Anyway, that's what I'm thinking. Hope this helps!
    Oh crap, yea you are correct. I totally forgot using the binomial formula in the exam! Well as an answer i got around 0.35 hopefully the professor does not mark it wrong. Thanks.

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats