A group of investors wants to develop a chain of fast-food restaurants. In determining potential costs
for each facility, they must consider, among other expenses, the average monthly electric bill. They
decide to sample some fast-food restaurants currently operating to estimate the monthly cost of
electricity. They want to be 90% confident of their results and want the error of the interval estimate to
be no more than $100. They estimate that such bills range from $600 to $2,500. How large a sample
should they take?
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