1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook