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Homework Help: Estimated probibility does not match results, why? (galaxies)

  1. Oct 6, 2011 #1
    1. The problem statement, all variables and given/known data

    my book states that approx 75% of galaxies in the universe are spirals, but then it says that out of a sample of 14 from the core of a large cluster of galaxies only 3 were found to be spiral.

    it was suggested we could use binomial distribution to look at the prob of seeing such small fractions in order to draw a conclusion.

    3. The attempt at a solution

    i showed binomial prob of seeing 3 was 3.66e-5, and that one would expect 10.5 spirals with a variance of 2.625. clearly this is based on the initial statement of 75% and that is of the whole galaxy, whereas we are looking at a cluster core. so i expect we should have a different prediction.

    but is there any other things that can be seen using the binomial distribution to discuss seeing such small fractions?

  2. jcsd
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