Binomial or permutation probability?

Question

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?

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?
@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.
@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.
@Quinn, I'm sure that can be arranged, although I'd prefer it be done elsewhere. Maybe there's an abuse.stackexchange site.

score 2 · Answer 1 · 2013-02-12 03:20:49Z

up vote 2 down vote

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

edited Feb 12 at 3:20

answered Feb 12 at 2:47

user4594

1

There is something to be said for leaving some work for OP, when it's a homework problem. – Gerry Myerson Feb 12 at 3:11

What more work do you want? Thats all of it. – CogitoErgoCogitoSum Feb 12 at 3:13

1 Answer