An urn contains three white and four black balls. We take out a ball and put it in a drawer without looking at it. After that we take out a second ball. Find the probability that this ball is white.

• let us assume that first ball drawn is white and second ball is also white OR first ball drawn is Black and second ball drawn is White
  so,
  W W OR B W
  probability of drawing first white ball = 3/7 as total 7 balls
  probability of drawing sec. white ball=2/6
  similarly probability of drawing first black ball =4/7
  then white ball = 3/6
  hence, total probability is
  3/7*2/6 + 4/7*3/6
  = 3/7
  =
• 10 years agoHelpfull: Yes(2) No(0)
• Ans 5/6
  (3C1+2C1)/(6C1)
• 10 years agoHelpfull: Yes(0) No(0)
• 2 cases-W,W AND B,W
  (3/7)*(2/6)+(4/7)*(3/6)=3/7
• 10 years agoHelpfull: Yes(0) No(0)
• 2 cases-W,W AND B,W
  (3/7)*(2/6)+(4/7)*(3/6)=3/7
• 8 years agoHelpfull: Yes(0) No(0)