Walmart Problem&Key.pdf

# A different number of lanes was opened each day the

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customer to go through the lane and complete the transaction. A different number of lanes was opened each day. The data is below. Date 11/22 11/23 11/29 11/30 12/6 12/7 12/14 12/15 12/21 12/22 12/29 12/30 Weather Sun Cloudy Sun Rain Sun Sun Cloudy Cloudy Cloudy Rain Snow Sun Lanes 5 12 11 7 12 8 6 10 8 6 4 8 Avg Wait Time (Min) 12.2 4.2 4.4 6.75 3.8 5.75 10.4 6.5 6.25 9.2 1.1 5.6 1. What is the explanatory variable? Lanes What is the response variable? Avg wait . 2. For answer # 1, make a scatterplot on your calculator and draw it below. x = lanes, y = avg wait 3. There is a clear outlier on your scatterplot. Circle it. 4. Give a reason that would justify eliminating the outlier. It was snowing. Few customers. 5. Generate the least squares regression line that describes the data (with the outlier eliminated). (2 dec places). ˆ y = " 0.96 x + 14.96 6. Give the meaning of the slope in the LSRL. For every extra lane open, .96 minute less of a wait. 7. What specific point is the LSRL guaranteed to go through? x , y ( ) = 8.45,6.82 ( ) 8. Describe the data in terms of form, direction, and strength. Fairly strong negative linear correlation 9. Find the value of r . r = " .88. Interpret it. Fairly strong negative linear correlation 10. Find the value of r 2 = .78. Interpret it. 78% of the variation in waiting time can be explained by the LSRL. 11. What is the predicted average waiting time if Walmart opens 9 lanes? 6.32 minutes 12. What is the predicted average waiting time if Walmart opens 7 lanes? 8.24 minutes 13. What is the difference between the actual waiting time and predicted waiting time for 7 lanes? " 1.5 min 14. If Walmart decides that it wants its customers to wait no longer than 4.5 minutes, how many lanes should it open? 11 lanes. 15. If Walmart decides that it wants its customers to wait no longer than 10 minutes, how many lanes should it open? 6 lanes 16. What is the predicted average waiting time if Walmart opens only one lane? 14 min. 17. What is the predicted average waiting time if Walmart opens 20 lanes? -4.24 min 18. Why do the last two problems and answers make little sense for this problem? Extrapolation is always dangerous. The minimum waiting time must be positive.

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Stu Schwartz On the same days of the previous problem, Walmart will need to hire extra staff to man the checkout lanes. They will have to pay out more money for the workers. The chart below describes how much money in pay it paid out during those hours on these specific days.
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• Fall '17

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