SOLUTION: In a shipment of 18 smart phones, 2 are defective. How many ways can a quality control inspector randomly test 4 smart phones, of which 2 are defective?

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Question 967414: In a shipment of 18 smart phones, 2 are defective. How many ways can a quality control inspector randomly test 4 smart phones, of which 2 are defective?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
18 phones total
16 nondefective
2 defective

Testing 4 phones: 2 defective, 2 nondefective

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Number of ways to pick 2 defective phones:

2 C 2 = (2!)/(2!*(2-2)!) = 1

I'm using the combination formula.

There is 1 way to pick 2 defective phones from a pool of 2 total defective phones.
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Number of ways to pick 2 nondefective phones

16 C 2 = (16!)/(2!*(16-2)!) = 120

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So there are 1*120 = 120 different ways to pick 4 smart phones, of which 2 are defective