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STS electricity cost probl

# STS electricity cost probl - New Mexico during the month of...

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The following frequency distribution reports the electricity cost for a sample of 50 twobedroom apartments in Albuquerque, N CI Midpoint (x) f fx d = x - x-bar d^2 fd^2 80-100 90 3 270 -51.2 2621.44 7864.32 100-120 110 8 880 -31.2 973.44 7787.52 120-140 130 12 1560 -11.2 125.44 1505.28 140-160 150 16 2400 8.8 77.44 1239.04 160-180 170 7 1190 28.8 829.44 5806.08 180-200 190 4 760 48.8 2381.44 9525.76 Sums = 50 7060 33728.00 Mean cost, x-bar = Sum(fx) / Sum(f) = \$141.20 Standard deviation of the cost = sqrt [sum(fd^2) / sum(f)] = \$25.97 Proportion of the costs within 2 standard deviations of the mean = Area under the standard

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Unformatted text preview: New Mexico during the month of May last year. Electricit cost frequency \$80-100 3 100-120 8 120-140 12 140-160 16 160-180 d normal curve from z = -2 to z = 2 = 0.95 0 7 180-200 4 Total= 50 a. Estimate the mean cost. b. Estimate the standard deviation. c. Use the Empirical Rule to estimate e the proportion of costs within two standard deviations of the mean. What are these limits?...
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