Question

Forbes Magazine lists the richest people in the world each year. The following data represents the ages of 40 of these individuals. All of these individuals have a net worth of at least $5 billion.

17        24        31        32        32        43        43        43

46        50        51        51        54        55        55        59

59        60        62        62        62        62        63        64

69        71        71        73        73        74        75        75

76        77        79        81        82        82        84        84

Use this sample of 40 billionaires to construct a 95% confidence interval for the mean age of all billionaires.

Answer 1

for above data:

sample mean 'x̄=	60.150 (from excel command average on above data)
sample size   n=	40.00
sample std deviation s=	17.380 (from excel command stdev on above data)
std error 'sx=s/√n=13.38/√40 =	2.748

for 95% CI; and 39 df, value of t=		2.023
margin of error E=t*std error    =		5.559
lower bound=sample mean-E =		54.59
Upper bound=sample mean+E =		65.709
from above 95% confidence interval for population mean =(54.59 billion to 65.71 billion)

(please try 54.76 to 65.54 if z distribution to be used with critical value of z =1.96)