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Pratibha’s desk has 8 drawers. When she receives a paper, she usually chooses a drawer at random to put it in. However, 2 out of 10 times she forgets to put the paper away, and it gets lost.

The probability that a paper will get lost is 2/10 , or 1/5 .

- What is the probability that a paper will be put into a drawer?

- If all drawers are equally likely to be chosen, what is the probability that a paper will be put in drawer 3?

When Pratibha needs a document, she looks first in drawer 1 and then checks each drawer in order until the paper is found or until she has looked in all the drawers.

1. If Pratibha checked drawer 1 and didn’t find the paper she was looking for, what is the probability that the paper will be found in one of the remaining 7 drawers?

2. If Pratibha checked drawers 1, 2 and 3, and didn’t find the paper she was looking for, what is the probability that the paper will be found in one of the remaining 5 drawers?

3. If Pratibha checked drawers 1–7 and didn’t find the paper she was looking for, what is the probability that the paper will be found in the last drawer?

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by omSanghvi

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