A meteorologist who sampled 4 thunderstorms found that the average speed at which they traveled across a certain state was 16 miles per hour. The standard deviation of the sample was 4.1 miles per hour. Round the final answers to at least two decimal places. Required:
Find the 90% confidence interval of the mean. Assume the variable is normally distributed.

The  90 % confidence  interval  for the mean population is (11.176  ; 20.824 )

Rounding to at least two decimal places would give 11.18 , 20.83

Step-by-step explanation:

Mean = x`= 16 miles per hour

standard deviation =s= 4.1 miles per hour

n= 4

 =  4.1/√4= 4.1/2= 2.05

1-α= 0.9

degrees of freedom =n-1=  df= 3

∈ ( estimator  t with 90 % and df= 3 from t - table ) 2.353

Using Students' t - test

x`±∈ *

Putting values

16 ± 2.353 * 2.05

= 16 + 4.82365

20.824  ;        11.176

The  90 % confidence  interval  for the mean population is (11.176  ; 20.824 )

Rounding to at least two decimal places would give 11.18 , 20.83

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