A group of investors wants to develop a chain of fast food cafés

A group of investors wants to develop a chain of fast food cafés. In determining potential costs for each facility, they must consider, among other costs, the average monthly cost of electricity. They want to be 90% confident of their results and want the error of 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?

Suppose a study reports that the average price per gallon of gas is $3.16. You believe that the figure is higher in your area. You decide to test this claim for your area by randomly calling gas stations. You randomly survey 25 stations producing the following prices (all in $). Assume gas prices for a region are normally distributed. Does the data you obtained provide enough evidence to reject the claim? Use a 1% level of significance. 
3.27
2.29
3.16
3.20
3.37
3.20
3.23
3.19
3.20
3.24
3.16
3.07
3.27
3.09
3.35
3.15
3.23
3.14
3.05
3.35
3.21
3.14
3.14
3.07
3.10

Where do CFOs get their money news? According to Robert Half International, 47% get their money news from the newspaper, 15% get it from peers, 12% get it from TV, 11% from the internet, 9% from magazines, 5% from radio! and 1% do not know. Suppose a researcher wants to test these results. She randomly samples 67 CFOs and finds that 40 of the get their info from newspapers. Does the test show enough evidence to reject the findings of Robert Half International? Use a= .05