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A box contains 3 defective batteries and 7 good ones. You reach in and pull out three

batteries. What is the expected number of defective batteries?

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Answer:

The expected number of defective batteries to be pulled out is 0.9, which rounded to the nearest integer gives a total of 1, that is, 1 of the 3 batteries is expected to be defective.

Explanation:

Given that a box contains 3 defective batteries and 7 good ones, and I reach in and pull out three batteries, to determine what is the expected number of defective batteries, the following calculation must be performed:

3 + 7 = 100

3 = X

10 = 100

3 = X

3 x 100/10 = X

300/10 = X

30 = X

3 x 3/10 = X

0.9 = X

Therefore, the expected number of defective batteries to be pulled out is 0.9, which rounded to the nearest integer gives a total of 1, that is, 1 of the 3 batteries is expected to be defective.

User Paul McMahon
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