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A marketing research company desires to know the mean consumption of milk per week among people over age 31. A sample of 343 people over age 31 was drawn and the mean milk consumption was 4.4 liters. Assume that the population standard deviation is known to be 0.9 liters. Construct the 90% confidence interval for the mean consumption of milk among people over age 31. Round your answers to one decimal place.

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Answer:

(4.3 ; 4.5)

Step-by-step explanation:

Given :

Sample size, n = 343

Sample Mean, xbar = 4.4

Standard deviation, σ = 0.9

Zcritical at 90%

Using the relation :

Xbar ± Margin of error

Margin of Error = Zcritical * σ/√n

Margin of Error = 1.645 * (0.9/√343)

Margin of Error = 0.0799394

Lower boundary = 4.4 - 0.0799394 = 4.320

Upper boundary = 4.4 + 0.0799394 = 4.480

(4.320 ; 4.480)

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