Posted by **Mike** on Sunday, February 20, 2011 at 7:04pm.

I need help on this question i am confused. I don't think the answers i got are right

The library checks out an average of 320 books per day, with a standard deviation of 75 books. Suppose a simple random sample of 30 days is selected for observation.

What is the probability that the sample mean for the 30 days will be between 300 and 340 books?

0.4279

0.2128

0.8558

0.1064

0.9279

There is a 90% chance that the sample mean will fall below how many books?

Answer

323.5

416.0

342.5

337.5

443.4

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