posted by .

if you randomly answer a t/f test and want to figure the possibililty of gettng at least an do you start and then once you have done this, what if you want to try it 4 more times? HELP

Let N be the number of questions. You are asking for the probability of getting N/5 or fewer wrong by randomly guessing.

Assume N>> 1 and use an error-function approximation for the number of questions answered correctly. The mean will be N/2 and the standard deviation will be sqrt[N*p*(1-p)] = (1/2)sqrtN, since p = 1/2 is the probability of getting each one right.
Inegrate the probability of correct answers from 0.8 N to N, which you can treat as infinity when N is very large.

The larger the value of N, the less likely you will be to get 80% right.

For N=25, I get a standard deviation of 2.5 about a mean of 12.5, and the probability of getting 20 or more right will be 0.0013. It becomes a much lower probability of N = 100. You need to use an error function table for this sort of problem.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. stats again

    ok I get it, so once I get the prob figred for one person, how do I figure it if additional attempts are made and the question is about the prob of at least one of the additional attempts say n = 6 getting the same results as the first …
  2. AP Statistics

    Of all U.S. fourth graders, 71% are assigned mathematics homework three or more times per week. If 5 fouth graders are randomly selected to be checked for this frequency of homework assignment during a randomly chosen week, find the …
  3. Stats

    A test has 15 true or false questions and 10 multiple choice questions (each with 4 choices). All questions are weighted equally. Jack has not studied at all for the test and randomly guesses. 1. What is the probability that Jack gets …
  4. Stats

    A group of 56 randomly selected students have a mean score of 30.8 and a standard deviation of 4.5 on a placement test. Find a 95% confidence interval for the mean score, ì, of all students taking the test. (Note: ó is unknown.)
  5. stats

    A study by Hewitt Associates showed that 79% of companies offer employees flexible scheduling. Suppose a researcher believes that in accounting firms this figure is lower. The researcher randomly selects 415 accounting firms and through …
  6. stats

    Test scores on a university admissions test are normally distributed, with a mean of 500 and a standard deviation of 100. 4 marks a. What is the probability that a randomly selected applicant scores between 425 and 575?
  7. Stats

    Find the P-value for a left tailed hypothesis test with a test statistic of z= -1.77. Decide wether to reject the null if the level of significance is alpha= 0.05. Please help I've tried everything and I can't figure out how to get …
  8. Math / Algebra

    Can you check my work? Thank you :) 1. The Domain of a function F is the same as the range of F^-1 (True or False?
  9. stats

    a captain claims that at least 85% of the residents in his barangay have household pets. to test this claim a researcher randomly selected a sample of 550 residents and find that 495 of them do have household pets. at 0.05 level of …
  10. English

    1. Try to do this at least 5 to 10 times. 2. Try to do this at least from 5 to 10 times. (Doe s#1 mean #2?

More Similar Questions