A bag contains 6 balls of one or more colours. A ball is picked and is found to be red. What is the probability that the bag initially had exactly 6 red balls?
option
a) 2/7
b) 1/5
c) 3/5
d) 4/5

• If we have 1 red ball then the probability of drawing 1 red ball out of 6 balls is 1/6
  
  If there are 2 red balls then the probability of drawing 1 red ball out of them is 2c1/6
  
  similarly the other cases 3/6 4/6 5/6 6/6..
  
  Now the probability of drawing 1 red ball when all the six are red is
  [6/6]/[(1/6)+(2/6)+(3/6)+(4/6)+(5/6)+(6/6)]
  6/21=2/7..
• 10 years agoHelpfull: Yes(15) No(10)
• tanu are this question asked in tcs ??????
  
• 10 years agoHelpfull: Yes(3) No(6)
• as we know, possibility of exactly 6 red ball is 1 and total possible outcomes is 6 because one ball is red (given) now 6 cases are..1) remaining 5 balls are also red 2) 4 out of the remaining 5 are red 3) 3 out of the remaining 5 balls are red 4) 2 out of the remaining 5 balls are red 5) 1 out of the remaining 5 balls are red 6) none out of 5 balls is red.....therefore-
  probability= 1/6.....therefore answer is none of these..
  
• 10 years agoHelpfull: Yes(2) No(4)
• can anyone explain it?
• 5 years agoHelpfull: Yes(0) No(0)