A drawer holds 4 red hats and 4 blue hats. What is the probability of getting exactly three red hats or exactly 3 blue hats while taking out 4 hats randomly out of the drawer and immediately returning every hat to the drawer before taking out the next?
option
A. 1/2
B. 1/8
C. 1/4
D. None of these

• possible ways
  one red (1/2) and 3 blue(1/2 * 1/2 *1/2)= 1/16
  one blue (1/2) 3 red (1/2 * 1/2 *1/2)= 1/16.
  
  so 'or'ing two conditions we get = 1/16 + 1/16 = 1/8 ans B
• 10 years agoHelpfull: Yes(22) No(12)
• 1/2
  
  p(drawing a red hat) = p(drawing a blue hat) = 4/8 = 1/2
  
  exactly 3 R in 4 draw:
  4 ways
  BRRR
  RBRR
  RRBR
  RRRB
  
  each of these have prob : 1/2 * 1/2 * 1/2 * 1/2 = 1/16
  
  thus p(drawing exactly 3 R hats) = 4 * 1/ 16 = 1/4
  
  similarly, p(drawing exactly 3B hats) = 1/4
  
  p(3 R or 3 B) = 1/4 + 1/4 = 1/2
• 10 years agoHelpfull: Yes(22) No(3)
• we also have to see the arrangement
  like RRRB+RBRR+RRBR+BRRR
  SIMILARLY FOR THE SECONDCASE OF BLUE
  So robability shud b
  4/16+4/16=1/2
• 10 years agoHelpfull: Yes(6) No(6)
• answer c.
  1/4
• 10 years agoHelpfull: Yes(5) No(9)
• probability of getting 1 red =4/8=1/2
  After replacement, again the probability of getting red is 1/2.
  
  probability for exactly 3 red=1/2*1/2*1/2=1/8
  Similarly probability for getting 3 blue after each replacement is also 1/8
  Total probability=1/8+1/8=1/4 Ans
• 10 years agoHelpfull: Yes(2) No(9)
• 1/2(ans)
  
  p(drawing a red hat) = p(drawing a blue hat) = 4/8 = 1/2
  
  exactly 3 R in 4 draw:
  4 ways
  BRRR
  RBRR
  RRBR
  RRRB
  
  each of these have prob : 1/2 * 1/2 * 1/2 * 1/2 = 1/16
  
  thus p(drawing exactly 3 R hats) = 4 * 1/ 16 = 1/4
  
  similarly, p(drawing exactly 3B hats) = 1/4
  
  p(3 R or 3 B) = 1/4 + 1/4 = 1/2
• 10 years agoHelpfull: Yes(2) No(3)