A subsonic wind tunnel operates 5 days a week. The electrical energy consumed on the 5 consecutive days is 120 kWh, 150 kWh, 135 kWh, 160 kWh, and 145 kWh. What is the sample standard deviation (in kWh) of this daily energy consumption? (Round off to two decimal places).

Answer Key:

15.21

### Solution: Mean $\bar{x} = \frac{120+150+135+160+145}{5} = \frac{710}{5} = 142\text{ kWh}$. Deviations: -22, 8, -7, 18, 3. Squared: 484, 64, 49, 324, 9. Sum = 930. Sample variance $s^2 = \frac{930}{5-1} = \frac{930}{4} = 232.5$. Sample standard deviation $s = \sqrt{232.5} \approx 15.2479 \approx 15.25\text{ kWh}$. Correct range: 15.20 to 15.30.

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