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In this module the student will explore the properties of data with a uniform distribution.

Student learning outcomes

  • The student will analyze data following a uniform distribution.

Given

The age of cars in the staff parking lot of a suburban college is uniformly distributed from six months (0.5 years) to 9.5 years.

Describe the data

What is being measured here?

The age of cars in the staff parking lot

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In words, define the Random Variable X size 12{X} {} .

X size 12{X} {} = The age (in years) of cars in the staff parking lot

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Are the data discrete or continuous?

Continuous

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The interval of values for x size 12{X} {} is:

0.5 - 9.5

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The distribution for X size 12{X} {} is:

X size 12{X} {} ~ U ( 0 . 5,9 . 5 ) size 12{U \( 0 "." 5,9 "." 5 \) } {}

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Probability distribution

Write the probability density function.

f ( x ) size 12{f \( x \) } {} = 1 9 size 12{ { {1} over {9} } } {}

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Graph the probability distribution.

  • Sketch the graph of the probability distribution.
  • Identify the following values:
    • Lowest value for x size 12{X} {} :
    • Highest value for x size 12{X} {} :
    • Height of the rectangle:
    • Label for x-axis (words):
    • Label for y-axis (words):
  • 0.5
  • 9.5
  • 1 9 size 12{ { {1} over {9} } } {}
  • Age of Cars
  • f ( x ) size 12{f \( x \) } {}
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Random probability

Find the probability that a randomly chosen car in the lot was less than 4 years old.

  • Sketch the graph. Shade the area of interest.
    Blank graph with vertical and horizontal axes.
  • Find the probability. P ( x < 4 ) size 12{P \( X<"5730" \) } {} =
  • 3 . 5 9 size 12{ { {3 "." 5} over {9} } } {}
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Out of just the cars less than 7.5 years old, find the probability that a randomly chosen car in the lot was less than 4 years old.

  • Sketch the graph. Shade the area of interest.
  • Find the probability. P ( x < 4 x < 7 . 5 ) size 12{P \( X<4 \lline X<7 "." 5 \) } {} =
  • 3 . 5 7 size 12{ { {3 "." 5} over {7} } } {}
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What has changed in the previous two problems that made the solutions different?

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Quartiles

Find the average age of the cars in the lot.

μ size 12{μ} {} = 5

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Find the third quartile of ages of cars in the lot. This means you will have to find the value such that 3 4 size 12{ { {3} over {4} } } {} , or 75%, of the cars are at most (less than or equal to) that age.

  • Sketch the graph. Shade the area of interest.
    Blank graph with vertical and horizontal axes.
  • Find the value k size 12{k} {} such that P ( x < k ) = 0 . 75 size 12{P \( X<k \) =0 "." "75"} {} .
  • The third quartile is:
  • k size 12{k} {} = 7.25
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Source:  OpenStax, Collaborative statistics. OpenStax CNX. Jul 03, 2012 Download for free at http://cnx.org/content/col10522/1.40
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