A group of developers wants to invest a chain of fast-food restaurants. In determining potential costs for each facility, they must consider among other expenses, the median 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% condfident 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 $2500. How large a sample should they take?
Note: There is a rule of thumb that says the standard deriation can be estimated as a quarter of the range.