Concept explainers
(a)
To find: the percent of large lids that are very small to fit.
(a)
Answer to Problem 56E
Approximately 6.7% of lids are too small.
Explanation of Solution
Given:
Mean diameter is 3.98 inches
Standard deviation is 0.02 inches.
Diameter is between 3.95 and 4.05 inches
Calculation:
If a lid is too small to fit, that means that its diameter is less than 3.95. Let x be the width of lid.
Find the proportion of lids for which
The graph below shows the area below 3.95
Find the z value corresponding to
From standard normal tables, the proportion of observations less than
So, approximately 6.7% of lids are too small.
Conclusion:
Therefore, 6.7% of lids are too small.
(b)
To find: the percent of large lids that are very big to fit.
(b)
Answer to Problem 56E
It is extremely rare for a lid to be too big.
Explanation of Solution
Given:
Mean diameter is 3.98 inches
Standard deviation is 0.02 inches.
Diameter is between 3.95 and 4.05 inches
Calculation:
If a lid is too large to fit, that means that its diameter is more than 4.05. Let x be the width of lid.
Find the proportion of lids for which
The graph below shows the area above 4.05:
Find the z value corresponding to 4.05 as follows:
From the standard normal tables, the proportion of observations less than 3.5 is approximately 1, so the proportion of observations greater than 3.5 is approximately 0.
Hence, it is extremely rare for a lid to be too big.
Conclusion:
Hence, it is extremely rare for a lid to be too big.
(c)
To compare: the answers to (a) and (b).
(c)
Answer to Problem 56E
It makes more sense to have a larger proportion of lids too small rather than too large.
Explanation of Solution
Given:
Mean diameter is 3.98 inches
Standard deviation is 0.02 inches.
Diameter is between 3.95 and 4.05 inches
Calculation:
It makes more sense to have a larger proportion of lids too small rather than too large. The company wants to make sure that the fit is snug. If more lids are too large, there will be more spills. If lids are too small, customers will just try another lid. But if lids are too large, the customer may not notice and then spill the drink.
Conclusion:
Therefore, it makes more sense to have a larger proportion of lids too small rather than too large.
Chapter 2 Solutions
The Practice of Statistics for AP - 4th Edition
Additional Math Textbook Solutions
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