Question

In: Statistics and Probability

12. A sample of 7 repair costs for smart phones have an average of $95.56 and...

12. A sample of 7 repair costs for smart phones have an average of $95.56 and a standard deviation of $20. Build the 90% confidence interval for the true average cost to repair a smart phone.

Solutions

Expert Solution

)Given that,

= 95.56

s =20

n = 7

Degrees of freedom = df = n - 1 =7 - 1 = 6

At 90% confidence level the t is ,

= 1 - 90% = 1 - 0.90 = 0.1

/ 2 = 0.1 / 2 = 0.05

t /2,df = t0.05,6=  1.943    ( using student t table)

Margin of error = E = t/2,df * (s /n)

=  1.943 * (20 / 7) = 14.7

The 90% confidence interval is,

- E < < + E

95.56 - 14.7 < < 95.56 + 14.7

80.86< < 110.26

orchestra answered 2 years ago
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