Practice prompt · Q:statistics-estimation-and-uncertainty/statistic-parameter-001

Label Juniper's observed and target means

Distinguish the known sample mean from the fixed but unknown population mean.

Updated Aug 7, 2026 Review due Nov 7, 2026

Practice

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The 16 selected Year 1 invoices have mean 31.875 days. The mean for all 480 qualifying Year 1 invoices is not disclosed. Which labels preserve the sample and population roles?

The distinction survives even when the sample is well selected and the point estimate is close to the parameter.

Choose the best answer. a Both means are statistics because both refer to numbers. b 31.875 days is the sample statistic x-bar; the fixed but unknown 480-invoice mean is the parameter mu. c 31.875 days is exactly mu because a random sample has no sampling variability. d The population mean varies every time a new sample is selected.

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Answer: b

Choice b. The observed 31.875-day x-bar is a statistic; mu denotes the fixed population quantity the sample may help estimate.