Question

A sample of 249 one-year-old baby boys in the United States had a mean weight of 24.2 pounds. Assume the population standard deviation is 4.7 pounds. What is the upper bound of the 90% confidence interval for the mean lifetime of the components?

Answer 1

The Confidence Interval formula is

X ± Z s/sqrt(n)

Where:

X is the mean

Z is the Z-value from the table below

s is the standard deviation

n is the number of observations

Z value

80% 1.282

85% 1.440

90% 1.645

95% 1.960

99% 2.576

99.5% 2.807

99.9% 3.291

90% Confidence Interval: 24.2 ± 0.49
(23.7 to 24.7)

"With 90% confidence the population mean is between 23.7 and 24.7, based on 249 samples."

Short Styles:
24.2 (90% CI 23.7 to 24.7)
24.2, 90% CI [23.7, 24.7]

Margin of Error: 0.49
(to more digits: 0.4899)