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Homework Help: I'm dumb I know, I need Probability help

  1. Mar 15, 2006 #1
    I did this problem but am not too sure it's right, have a look

    Of all households making less than $25,000 annually, 45% of them use coupons weekly when shopping for groceries. Suppose 10 households making less than $25,000 annually are selected at random. What is the variance of the number of households that use coupons weekly?

    I got 4.5

    But I have no clue how to do this one, the book doesn't explain anything

    Suppose 30% of all M&Ms are brown. If 7 M&Ms are randomly selected, what is the probability that at most 1 is brown?
     
  2. jcsd
  3. Mar 16, 2006 #2

    HallsofIvy

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    Science Advisor

    These are both binomial distribution problems. The probability that a selected house hold uses coupons weekly is 0.45 and the probability that is does not is 0.55. You should have a formula for the variance of a sample from a binomial distribution.

    If 30% of all M&Ms are brown, then 70% are not- the chance that any randomly selected M&M is not brown is 0.7. What is the probability that all 10 are not brown? What is the probability that exactly one is brown?
    Again, this is a binomial distribution.
     
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