# Probability when seleting balls from an urn

1. May 18, 2010

### dperkovic

1. The problem statement, all variables and given/known data

There is total of 300 balls in the basket, 30 of them is red (rest is white). If we picked up, randomly, 4 balls, what is the probabilty that all of them is red ?

2. The attempt at a solution

For one picked ball, probability that it's red is 30/300 = 1/10.
If picked ball is red, probabilty for next ball is 29/299,and so on, 28/298, 27/297.

Is that correct ? And, what next ?

2. May 18, 2010

### Maybe_Memorie

Re: Probability

Yup, thats right so far.
In probability, what is the relationship with "And" events?

3. May 18, 2010

### dperkovic

Re: Probability

P(A and B) = P(A) x P(B) ???

4. May 18, 2010

### dperkovic

Re: Probability

P(A and B) = P(A) x P(B after A) is correct,because this is depended events, is that true ?

If it is, the solution would be: 30/300 * 29/299 * 28/298 * 27/297.

5. May 18, 2010

### Maybe_Memorie

Re: Probability

Exactly.