16Hit1600
Problem-Solving and Data AnalysisMediumUpper end of a plausible interval

Problem-Solving and Data Analysis practice question

A random sample of 150 loaves from a bakery has a mean mass of 812 grams, and the associated margin of error is 9 grams. Based on this sample, what is the greatest plausible value, in grams, of the mean mass of all loaves the bakery produces?

Answer: 821

The plausible range for the population mean runs from 812 − 9 to 812 + 9, that is, 803 to 821 grams. The greatest plausible value is 821.

Common wrong answers

If you answered 803
803 is the LOWER end of the interval (812 − 9). The greatest plausible value adds the margin.
If you answered 812
812 is the sample mean itself. The margin of error extends the plausible range 9 grams above it.
If you answered 830
830 adds the margin twice (812 + 18). The interval is the mean plus or minus ONE margin of error.

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