School

Iowa State UniversityDepartment

StatisticsCourse Code

STAT 101Professor

Stephenson RobertLecture

13This

**preview**shows page 1. to view the full**4 pages of the document.**Statistics 104 - Laboratory 8

Normal Models

Often a population will have a variable whose distribution can be modeled using a normal

model with a population mean μ and a population standard deviation σ.

1. Market weight of gilts.

The market weight, in pounds, of 179 gilts, female hogs is displayed in the histogram

below.

10

20

30

40

50

Count

150 200 250 300 3

a) Describe the shape of the distribution. Why is a normal model a reasonable

model for the distribution of the population of gilt market weights?

b) Use a normal model for the population of gilt market weights with population

mean μ = 236.5 pounds and population standard deviation σ = 31.2 pounds to find

• The probability that a gilt market weight will be less than 300 pounds.

• The probability that a gilt market weight will be greater than 275 pounds.

• The probability that a gilt market weight will be between 200 and 300

pounds.

• The value such that 4% of all gilt market weights will be less than that

value.

• The value such that 25% of all gilt market weights will be greater than that

value.

• The values such that the middle 90% of all gilt market weights will fall

between those values.

Market Weight (lbs)

1

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