Question 970092: A package contains 12 resistors, 3 of which are defective. If 4 are selected, find the probability of getting two
defective resistors when the selection is done one after the other without replacement.
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Probability of 2 defective resistors.
There are 6 possible ways: first and second, first and third, first and fourth, second and third, second and fourth, third and fourth.
Look at the first two.
(3/12)*(2/11)*(9/10)*(8/9)
(3/12)*(9/11)*(2/10)*(8/9)
Notice, that each of these has the same product in the numerator and in the denominator. They aren't necessarily matched with the same denominator. Therefore, take the product of one of these and multiply by 6.
(432)*6/11880
= 2592/11880
P=0.2181 or P=0.22
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