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October 12th, 2013, 02:06 AM   #1
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A box contains 3 white, 8 red, 9 blue

Hi

1) A box contains 3 white, 8 red, 9 blue balls. If 3 balls are selected at random, find the probability
A) one ball of the each colour is selected
B) all balls are of the same colour
C) one red and two of any colour
D) All 3 are red
E) at least 1 is white
F) the balls are drawn in the order red, white, blue.
H) Two Balls are red

2) A box contain 4 bad 6 good tubes. Two are drawn from the box at a time.
What is the probability
A) that both the tubes drawn are good?
B) one is good and other is bad?
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October 12th, 2013, 03:49 AM   #2
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Re: A box contains 3 white, 8 red, 9 blue

I elaborate you the 2B, the others are similar.

definition of the probability in general:
  • p = number of the questioned cases / number of all cases
in this case:
  • p = number of one good and one bad drawn / number of 2 balls drawn from 10
that is:
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October 12th, 2013, 05:12 AM   #3
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Re: A box contains 3 white, 8 red, 9 blue

For the first question, let's begin with part A).

How many ways are there to draw one ball of each color? How many ways are there in total to choose 3 balls from the total of 20?
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October 12th, 2013, 01:54 PM   #4
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2(A) In this earlier topic, the probability that both tubes drawn are good was found to be 1/3.

2(B) Similarly, the probability that both tubes drawn are bad is 2/15, so the required probability is 1 - 1/3 - 2/15 = 8/15.
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