Question 1169358: A box contains 24 bulbs, 4 of which are defective. If 4 are sold at random, find the probability that exactly 2 are defective?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! 24C4 number of ways to sell 4
2 are defective is 4C2
what is left over is 20C2
probability is 4C2*20C2/24C4
=0.1073
can also do it with probability 1 and 2 are defective and 3 and 4 are not. Get different orders of numbers but 6 overall that are the same
(4/24/)(3/23)(20/22)(19/21)=0.01788
and this happens 6 different ways, but the numbers, while ordered differently, have the same products, and that equals the answer above.
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