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The mean replacement time for a random sample of 15 washing machine is 10.7 years and...

The mean replacement time for a random sample of 15 washing machine is 10.7 years and the standard deviation is 2.5 years. Construct 98% confidence interval for the standard deviation of the replacement of all washing machines of this type. What would be the value if the standard deviation is 2.7 years.

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Answer #1

Now , df=degrees of freedom=n-1=15-1=14

The critical values are ,

; The Excel function is , =CHIINV(0.01,14)

; The Excel function is , =CHIINV(0.99,14)

Therefore , the 98% confidence interval for the standard deviation of the replacement of all washing machines of this type is ,

Now , the null and alternative hypothesis is ,

Decision : Here , the value of the lies in the interval (1.73,4.49)

Therefore , fail to reject Ho.

i.e. the value of the standard deviation is 2.7 years.

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