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## Homework Statement

Each of 12 refrigerators of a certain type has been returned to a distributor because of the presence of a high pitched oscillating noise. Suppose that 5 of these 12 have defective compressors and the other 7 have less serious problems. If they are examined in random order, let X = the number among the first 6 examined that have a defective compressor. Compute the following:P(x = 1)

E(X)

E(X^2)

## Homework Equations

## The Attempt at a Solution

I'm getting really hung up here. I know my sample size is 6 refrigerators. 5 of the twelve are defective. My chances of picking a defective unit on the first try is 5/12.Someone told me that it was [(5 choose 3)(7 choose 3)]/(12 choose 6). I just don't understand how to do this well enough, so I don't know if it is the right answer or not. And I want to know how to do it anyway.