The following frequency distribution reports the electricity cost for a sample o

Question

The following frequency distribution reports the electricity cost for a sample of 50 two-bedroom apartments in Albuquerque, New Mexico, during the month of May last year. Estimate the mean cost. (Round your answer to 2 decimal places.) Mean cost Estimate the standard deviation. (Do not round intermediate calculations. Round your answer to 2 decimal places.) Standard deviation Use the Empirical Rule to estimate the proportion of costs within two standard deviations of the mean. What are these limits? (Round your answers to 2 decimal places.) Limits are from $ to $.

Explanation / Answer

First you should calculate mid points of given classes likewise (80+100)/2 = 90, (100+120)/2 = 110..............(180+200)/2 = 190.

a. Estimate the mean cost.
mean = [3*90+8*110+12*130+16*150+7*170+4*190)/(sum of the freqs) = 141.2

b. Estimate the standard deviation, s = 25.97.

c. Use the Empirical Rule to estimate the proportion of costs within two standard deviations of the mean. What are these limits?

mean - 2*S = 141.2-2*25.97 = 89.26 and

mean + 2*S = 141.2-2*25.97 = 193.15

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