Probability of balls chosen from an urn

[Gott_ist_tot]

Homework Statement

An urn contains 3 white and 4 red balls. A ball is chosen at random ( in a frequency sense) and replaced. What is the probability of the first 5 balls chosen exactly 2 will be white.

Homework Equations

The Attempt at a Solution

Really I haven't made much progress. I do not understand the significance of the balls being replaced. If they weren't replaced that would make sense to me. But with them being replaced I have no idea. Thanks for any help and advice.

 

[nicksauce]

Because they are being replaced, the chance of getting a white ball will always be 3/7.

So it's like, what is the probability that if you flip a coin 5 times you will get exactly two heads (only instead of 50/50, then chance of getting heads in 3/7).

 

[Dick]

The significance of the balls being replaced just means every time you draw a ball you have a 3/7 chance of it's being white and 4/7 of it's being red. So what are the odds of getting 2 white and 3 red. Binomial distribution. Go for it Nietzsche!