A bag contains 5 balls and it is not known how many of them are blue in colour. If 2 balls are drawn and found to be blue, then the probability that all the balls in the bag are blue is

1) 1/4
2) 1/2
3) 2/5
4) none of these

• P(2/5) =(2C2)/(5C2) =1/10
  P(3/5) = 3C2/5C2 =3/10
  P(4/5) = 4C2/5C2 = 6/10
  P(5/5) =5C2/5C2 = 1
  
  Hence required conditional probability = p(5/5)/{p(2/5)+...p(5/5)} = 1/(1/10+3/10+6/10+10/10)
  
  = 1/2.
• 12 years agoHelpfull: Yes(0) No(0)