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Answer:
(6290.678 ; 7790.742)
Step-by-step explanation:
Given the data :
5640, 5090, 6590, 6380, 7165, 8440, 9980
The sample mean, xbar = Σx / n = 49285 / 7 = 7040.71
The 90% confidence interval :
Xbar ± Margin of error
Margin of Error = Zcritical * σ/√n
Since the σ is known, we use the z- distribution
Zcritical at 90% confidence = 1.64
Hence,
Margin of Error = 1.64 * 1210/√7
Margin of Error = 750.032
90% confidence interval is :
7040.71 ± 750.032
Lower boundary = 7040.71 - 750.032 = 6290.678
Upper boundary = 7040.71 + 750.032 = 7790.742
(6290.678 ; 7790.742)