# Qnt Week 1

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Exercises 80, 82, and 87 (Ch. 3)

80. Please refer to excel sheet

82. 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.

a. Estimate the mean cost.

b. Estimate the standard deviation.

c. Use the Empirical Rule to estimate the proportion of costs within two standard deviations

of the mean. What are these limits?

Electricity cost frequency

80 to 100 3

100 to 120 8

120 to 140 12

140 to 160 16

160 to 180 7

180 to 200 4

total 50

Apartments:

Mean = (3*90 + 8*110 + 12*130 + 16*150 + 7*170 + 4*190)/50

= 141.2

Stdev = sqrt((3*(90-141.2)^2 + 8*(110-141.2)^2 + 12*(130-141.2)^2 + 16*(150-141.2)^2 + 7*(170-141.2)^2 + 4*(190-141.2)^2)/49)

Empirical rule, 2 stdevs is 95% of the data

141.2 - 2*26.236 to 141.2 + 2*26.236

88.728 to 193.672

87. Please refer to excel sheet

Exercises 34, 36, and 38 (Ch. 5)

34.

36. Dr. Stallter has been teaching basic statistics for many years. She knows that 80 percent of the students will complete the assigned problems. She has also determined that among those who do their assignments, 90 percent will pass the course. Among those students who do not do their homework, 60 percent will pass. Mike Fishbaugh took statistics last semester from Dr. Stallter and received a passing grade. What is the probability that he completed the assignments?

P = .80*.90 / (.20*.60 + .80*.90)

(calculator)

P = 0.857

38. One-fourth of the residents of the Burning Ridge Estates leave their garage doors open when they are away from home. The local chief of police estimates that 5 percent of the garages with open doors will have something stolen, but only 1 percent of those closed will have something stolen. If a garage is robbed, what is the probability the doors were left open?

We need:

prob(open | robbed)

Using...

Qnt Week 2