statistics

posted by .

It is known that 60% of people do not respond to mailed questionnaires. In a sample of 20 questionnaires mailed, what is the probability that more than 12 people will respond?

  • statistics -

    probability that 13 respond
    p(13)= C(20,13) (.4^13) (.6^7)
    = 77520 * 6.71 * 10^-6 * 2.8 * 10^-2
    = 1.46 * 10^-2
    and for 14
    p(14) = C(20,14)(.4^14)(.6^6)
    38760 * 2.68 * 10^-6 * 4.67 *10^-2
    =.485 * 10^-2
    etc for binomial distribution
    p(15) = 15504 * .4^15 * .6^5
    = .129 * 10^-2
    p(16) = 4845 *.4^16 *.6^4
    = .027 *10^-2
    p(17) = 1140 * .4^17 * .6^3
    =.0042 *10^-2
    p(18) = 190 * .4^18 * .6*2
    =.00047 *10^-2
    forget p(19) and p(20), getting too small
    add them up
    2.1*10^-2 = .02

  • statistics -

    By the way, n = 20 is high enough so we could use the continuous version, the normal distribution, to approximate and see if we are way off base.
    mean no response = 20 * .6 = 12
    sigma = sqrt (20*.6*.4) = 2.2
    To get more than 12 responding on the continuous distribution we want to be between 12 and 13 responding or between 7 and 8 not responding, call it 7.5
    (7.5-12)/2.2 = -2 sigmas from mean
    which is .023 in table of F(z) versus z on normal function table.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Statistics

    From: Siegel, A.F. (1997). Practical Business Statistics, 3rd Edition. Irwin/McGrawHill. Case - Can This Survey Be Saved?
  2. Statistics

    From: Siegel, A.F. (1997). Practical Business Statistics, 3rd Edition. Irwin/McGrawHill. Case - Can This Survey Be Saved?
  3. Math

    In 2001, credit card companies mailed 5 billion credit card applications to 262 million people. On average, how many applications were mailed to each person?
  4. stat

    A MAIL-ORDER FIRM HAS A CIRCULAR WHICH ELICITS A 10 % RESPONSE RATE. SUPPOSE 20 OF THE CIRCULARS ARE MAILED AS A MARKET TEST IN A NEW GEOGRAPHIC AREA. ASSUMING THAT THE 10% RESPONSE RATE IS APPLICABLE IN THE NEW AREA, DETERMINE THE …
  5. stat

    Problem 2. THE PROBABILITY THAT A RANDOMLY CHOSEN SALES PROSPECT WILL MAKE A PURCHASE IS 0.20. IF A SALESMAN CALLS ON SIX PROSPECTS, A. WHAT IS THE PROBABILITY THAT HE WILL MAKE EXACTLY FOUR SALES?
  6. statistics

    Suppose that a marketing firm sends questionnaires to two different companies. Based on historical evidence, the marketing research firm believes that each company, independently of the other, will return the questionnaire with a probability …
  7. statistics

    Suppose that a marketing firm sends questionnaires to two different companies. Based on historical evidence, the marketing research firm believes that each company, independently of the other, will return the questionnaire with a probability …
  8. STATISTICS

    True or False? A researcher is interested in studying whether there is a correlation of IQ with health. For this purpose he selected a sample of 261 people and asked them to complete two questionnaires: one for IQ and one for health.
  9. epidemiology

    In another study, the smoking habits of 34,445 male physicians were obtained by mailed questionnaires. Deaths among these physicians over the subsequent years were identified though contact with the office of the Registrar General. …
  10. Science

    A good business letter should A)Be printed and mailed B)Be professional and polite C)Demand actions from people in power D)Never be sent to people who are not interested in the topic. My answer B

More Similar Questions