If a bag contains 5 White Balls 6 Red Balls and 9 Black Ball

If a bag contains: 5 White Balls, 6 Red Balls, and 9 Black Balls, what is the probability of pulling out: A black or white ball A white ball A white ball and then a black ball without replacement? A white ball and then a black ball with replacement?

Solution

a)P [ a black or white ball ]

= ( 9 / 20 ) + ( 5 / 20) = 14 / 20 = 7 /10 = 0.7...

B) A white ball

= 5/ 20 = 1 /4 = 0.25....

c) A white ball and then a black ball without replacement

= ( 5 /20) * ( 9 / 19 ) = 9 / 76...

d) a white ball and then black with replacement

= ( 5 /20) * ( 9 / 20) = 9 / 80.....