Probability of draws without replacement. please help! I'm stuck!

Question

An urn contains red balls and white balls. If Frank chooses balls at random from the urn, what is the probability that he will select red balls and white balls? Round your answer to decimal places.

Answer 1

Mike,

         The number of ways of choosing 5 reds from 6 is ₆C₅=6. the number of ways of choosing 4 whites from 9 is ₉C₄=126

        So the number of possible successes is 6*126=756 i.e each one of these combinations will have 5 red and 4 white balls. Now the total number of ways of choosing 9 balls out of 15 is ₁₅C₉=5005 so the probability is P=# successes/total number= 756/5005=.151 or 15.1%

 

Hope this helps

 

Jim