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A company manufacturing a roadside lighting system wants to estimate the average illuminance (brightness) at sunset. The illuminance at sunset for the past 10 days was as follows: 406, 385, 389, 383, 352, 379, 388, 343, 368, 387 lux. Construct a 95% confidence intervals for the average illuminance at sunset. Assume that the illuminance at sunset is approximately normally distributed.

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Answer:

(364.595 ; 391.405)

Step-by-step explanation:

Given the sample data:

406, 385, 389, 383, 352, 379, 388, 343, 368, 387

Using calculator :

Sample mean, xbar = 378

Standard deviation, s = 18.74

Confidence interval :

Xbar ± Margin of error

Margin of Error = Tcritical * s/√n

TCritical at df = 24 ; 0.05 = 2.262

Margin of Error = 2.262 * 18.74/√10 = 13.405

Lower boundary = (378 - 13.405) = 364.595

Upper boundary = (378 + 13.405) = 391.405

(364.595 ; 391.405)

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