A bag contains 5 white balls and some black balls. If the probability of drawing a black ball from the bag is twice the probability of drawing a white ball then find the number of black balls.

• Let number of black balls be x,so total number of balls in the bag is x+5.
  P(black)=x/x+5
  p(white)=2*(5/x+5)
  x/x+5=2*(5/x+5)
  Solving this we get x as 10
  Number of black balls is 10
• 11 years agoHelpfull: Yes(1) No(0)
• p(b)=2*p(w)
  here white ball=5
  let black ball=x
  x/(5+x)=2*5/(5+x)
  i.e x=10
• 11 years agoHelpfull: Yes(0) No(0)
• let x no. of black ball,5 no of white ball
  so given p(b)=2*p(w)
  => x/x+5=2*5/5+x;
  =>x=10
  
• 11 years agoHelpfull: Yes(0) No(0)