Household spending on fuel

Topic: Estimation examples · more questions on this topic
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A sample of 51 households spends $1136 a year on petrol and heating oil on average, with sample standard deviation $178. Construct a 99% confidence interval for the mean annual spending. Use t_{50,\,0.995}=2.678.

Worked answer (click to show)

1136\pm 2.678\times\frac{178}{\sqrt{51}}=1136\pm 66.8,

which is (1069.2,\,1202.8).