Results 1 to 4 of 4

Math Help - Probability + normal distribution

  1. #1
    Newbie
    Joined
    Nov 2008
    Posts
    2

    Probability + normal distribution

    so my take-home quiz consists of a problem that i haven't been able to figure out, and i met similar frustration from my classmates as well.

    we are studying normal distribution as of now, and what seems a binomial problem this is a hard nut to crack:

    " a multiple choice test consists of 60 questions. each question has 4 possible answers of which one is correct. if all answers are random guesses, estimate the probability of getting at least 20% correct. "

    also, the instructions indicate to find the probability using the normal distribution as an approximation to the binomial distribution.

    my guesses are as follows:

    1. find z-score and use table, but i think it's out of the question to calculate standard deviation in this case

    2. use normalpdf or binomial pdf using TI-83 (n=60, p=.25) but really, have no idea where to go from there

    3. make a chart of x and P(x), or all outcomes on my TI-83 with binomial values and calculate standard deviation.

    please lead me in the right direction. i don't really need the answer, i just need to figure out how to get it!

    thank you in advance
    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 hopespaul View Post
    so my take-home quiz consists of a problem that i haven't been able to figure out, and i met similar frustration from my classmates as well.

    we are studying normal distribution as of now, and what seems a binomial problem this is a hard nut to crack:

    " a multiple choice test consists of 60 questions. each question has 4 possible answers of which one is correct. if all answers are random guesses, estimate the probability of getting at least 20% correct. "

    also, the instructions indicate to find the probability using the normal distribution as an approximation to the binomial distribution.

    my guesses are as follows:

    1. find z-score and use table, but i think it's out of the question to calculate standard deviation in this case

    2. use normalpdf or binomial pdf using TI-83 (n=60, p=.25) but really, have no idea where to go from there

    3. make a chart of x and P(x), or all outcomes on my TI-83 with binomial values and calculate standard deviation.

    please lead me in the right direction. i don't really need the answer, i just need to figure out how to get it!

    thank you in advance
    Are you familiar with the normal approximation to the binomial distribution? If so, where do you get stuck using it? If not, read this: Binomial distribution - Wikipedia, the free encyclopedia (5.2) and then state where you're stuck if you still are.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2008
    Posts
    2
    i know some about it, but i'm not exactly sure how to calculate the z-score of the 20th percentile
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by hopespaul View Post
    i know some about it, but i'm not exactly sure how to calculate the z-score of the 20th percentile
    Find the value of z* such that Pr(Z < z*) = 0.2.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Probability - Normal Distribution
    Posted in the Advanced Statistics Forum
    Replies: 5
    Last Post: March 8th 2010, 01:41 AM
  2. normal probability distribution
    Posted in the Statistics Forum
    Replies: 2
    Last Post: November 21st 2009, 10:50 PM
  3. by a normal probability distribution?
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: October 2nd 2009, 10:20 PM
  4. normal distribution probability
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: September 10th 2009, 07:58 PM
  5. normal distribution and probability
    Posted in the Statistics Forum
    Replies: 4
    Last Post: March 13th 2007, 06:47 PM

Search Tags


/mathhelpforum @mathhelpforum