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Class is over! Mr. Shrager does not always let his statistics class out on time. In fact, he seems to end class according to his own 鈥渋nternal clock.鈥 The density curve models the distribution of the amount of time after class ends (in minutes) when Mr. Shrager dismisses the class. (A negative value indicates he ended class early.)

a. What height must the density curve have? Justify your answer.

b. About what proportion of the time does Mr. Shrager dismiss class within 1 minute of its scheduled end time?

c. Calculate and interpret the 20thpercentile of the distribution.

Short Answer

Expert verified

Part (a) Height of the density curve is 0.2

Part (b) Mr. Sharger dismisses the class about 0.40 of the time within 1 minute of its scheduled end time.

Part (c) 20th percentile of the distribution is 0 minutes.

Step by step solution

01

Part (a) Step 1: Given information

The uniform distribution on interval 1x4 was used to simulate the distribution.

Such that

a=1

And

b=4

02

Part (a) Step 2: Concept

A density curve is always on or above the horizontal axis.

03

Part (a) Step 3: Calculation

The density curve is reciprocal to the difference in the borders in a uniform distribution.

In the space between the two limits,

f(x)=1b-a=14-(-1)=14+1=15=0.2

With

鈭1 鈮 x 鈮 4

f(x) represents the height of the density curve.

Thus, the height of the density curve is 0.2

b=4

04

Part (b) Step 1: Calculation

The likelihood that the dismissal time occurs between 1<X<1will be the area beneath the density curve between 1<X<1

Note that

The rectangle will be the area beneath the density curve.

With

Width, W=1(1)=1+1=2

And

Height, H=f(x)=0.2

Then

P(1<X<1)=Areaofrectangle=WH=20.2=0.4

Therefore,

Mr. Sharger dismisses the class about 0.40of the time within 1minute of its scheduled end time.

05

Part (c) Step 1: Calculation

20 percent of the data values should be smaller than the 20th percentile, according to the attribute for the 20th percentile.

Let

x be the 20th percentile.

The likelihood that the time is between the lower boundary and x will equal the area beneath the density curve between -1 and x

Note that

The rectangle will be the area beneath the density curve.

With

Width, W=x(1)=x+1

And

Height, H=f(x)=0.2

Then

P(X<x)=P(1<X<x)=Areaofrectangle=WH=(x+1)0.2=0.2x+0.2

We know that

x is the 20th percentile.

Then

The probability has to be equal to 20% or 0.2

0.2x+0.2=0.2

Subtract 0.2 from both sides.

0.2x=0

Divide the above equation by 0.2

That becomes

x=0/0.2=0

Therefore,

The 20th percentile of the distribution will be 0 minutes, which means that Mr. Shrager dismisses the class about 20% early of the time.

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