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Using Minitab for a Normal Probability Plot
A6.2 MINITAB
Using Minitab to Compute Normal
Probabilities
You can use Minitab instead of Table E.2 to compute normal probabilities. To find the probability that a download
time is less than 9 seconds with µ = 7 and σ = 2:
To construct a normal probability plot in Minitab for the 2003
returns of mutual funds, open the MUTUALFUNDS2004.MTW
worksheet. Then,
1. Select Graph Probability Plot.
2. In the Probability Plots dialog box, select Single. Click
the OK button.
3. In the Probability Plot-Single dialog box (see Figure
A6.2), in the Graph variables: edit box, enter C7 or
‘Return 2003’.
1. Enter 9 in the first row of column C1 of a blank
worksheet.
2. Select Calc Probability Distributions Normal.
3. In the Normal Distribution dialog box (see Figure A6.1)
select the Cumulative probability option button. Enter
7 in the Mean: edit box and 2 in the Standard deviation:
edit box. Select the Input column: option button and
enter C1 in its edit box. Click the OK button. You will
get the output displayed in the top portion of Figure
6.19 on page 206.
FIGURE A6.2 Minitab Probability Plot-Single Dialog
Box
4. Click the Distribution button. In the Probability Plot Distribution dialog box (see Figure A6.3), select
Normal in the Distribution drop-down list box. Click
the OK button to return to the Probability Plot - Single
dialog box. Click the OK button.
FIGURE A6.1 Minitab Normal Distribution Dialog
Box
To find the Z value corresponding to a cumulative area
of 0.10,
1. Enter .10 in row 1 of column C2.
2. Select Calc Probability Distributions Normal.
3. Select the Inverse cumulative probability option button. Enter 7 in the Mean: edit box and 2 in the Standard
Deviation: edit box.
4. Select the Input Column option button and enter C2
in the edit box. Click the OK button.
You will get the output displayed in the bottom portion
of Figure 6.19 on page 206.
FIGURE A6.3 Minitab Probability Plot-Distribution
Dialog Box
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CHAPTER SIX The Normal Distribution and Other Continuous Distributions
Using Minitab to Compute Exponential
Probabilities
To compute exponential probabilities for the ATM customer-arrival example using Minitab,
1. Enter .1 in column C1 of a blank worksheet.
2. Select Calc Probability Distributions Exponential.
3. In the Exponential Distribution dialog box (see Figure
A6.4), select the Cumulative probability option button. In the Scale: edit box, enter .05. This entry is made
because Minitab defines the mean as the mean time
between arrivals, 1/λ = 1/20 = 0.05, not the mean number of arrivals, λ = 20. Select the Input column:
option button and enter C1 in the Input column: edit
box. Click the OK button.
FIGURE A6.4 Minitab Exponential Distribution Dialog
Box