# Binomial or permutation probability?

A bowl contains 20 white balls, 10 red balls, and 10 blue balls. Assuming replacement, what is the probability you draw three red balls in a row?

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Can you see the balls before you draw them? Are some of the balls bigger than others? Do you get a bonus for picking three red ones? Are you allowed to stick something onto a ball before replacing it? – Gerry Myerson Feb 12 '13 at 3:10
@CogitoErgoCogitoSum You are hilariously irascible. – Quinn Culver Feb 12 '13 at 14:33
@Quinn, you may find it hilarious when one poster writes that another is acting like a moron, but that sort of personal abuse is not tolerated here, and this website is the better for that. Mature people can have disagreements without stooping to name-calling. – Gerry Myerson Feb 13 '13 at 5:57
@CogitoErgoCogitoSum: Here are what I think Gerry Myerson intended: "Can you see the balls before you draw them? Are some of the balls bigger than others? Do you get a bonus for picking three red ones?" These ask is the choice of one ball is as likely as any another? "Are you allowed to stick something onto a ball before replacing it?" This asks is the choice of one ball independent of the choice of the previous balls? I would have asked differently, but the question is terse and shows no effort by the OP. However, personal attacks and insults are not necessary or welcome. – robjohn Feb 13 '13 at 14:07
@Quinn, I'm sure that can be arranged, although I'd prefer it be done elsewhere. Maybe there's an abuse.stackexchange site. – Gerry Myerson Feb 14 '13 at 22:54

The probability assuming replacement is $\frac{10}{20+10+10}\times\frac{10}{20+10+10}\times\frac{10}{20+10+10}$.