Question

Following are weights, in pounds, of two-month-old baby girls. It is reasonable to assume that the population is approximately normal.

12.32 11.87 12.34 11.48 12.66
8.51 14.13 12.95 9.34 8.63

Required:
a. Construct a interval for the mean weight of two-month-old baby girls.
b. According to the National Health Statistics Reports, the mean weight of two—month-old baby boys is 13.9 pounds. Based on the confidence interval, is it reasonable to believe that the mean weight of two-month—old baby girls may be the same as that of two-month-old baby boys? Explain.

Answer 1

10.224 < μ < 12.622 ;

Since the mean weight of 2-montj old baby boys (13.9) falls outside the confidence interval, we can conclude that it is not reasonable to believe that the mean weight of two-month-old baby girls may be the same as that of two-month-old baby boys.

Explanation:

The confidence interval is given as :

Mean ± Margin of Error

margin of error = Zcritical * standard deviation /sqrt(n)

n = sample size

From the data:

12.32, 11.87, 12.34, 11.48, 12.66, 8.51, 14.13, 12.95, 9.34, 8.63

From the data:

Using calculator :

Mean, = 11.423

Standard deviation, s = 1.934

Zcritical at 95% confidence interval = 1.96

Sample size, n = 10

Margin of Error = 1.96* 1.934/sqrt(10) = 1.199

Lower boundary = 11.423 - 1.199 = 10.224

Upper boundary = 11.423 + 1.199 = 12.622

10.224 < μ < 12.622

Since the mean weight of 2-montj old baby boys (13.9) falls outside the confidence interval, we can conclude that it is not reasonable to believe that the mean weight of two-month-old baby girls may be the same as that of two-month-old baby boys.