20) A random sample of 42 light bulbs has a mean life of 645 hours with a standa
ID: 3051326 • Letter: 2
Question
20) A random sample of 42 light bulbs has a mean life of 645 hours with a standard deviation of 34 hours a) (4pts) Find the critical values for c-94. 8 34 invhom ± 1.8807 us b) (4pts) Find the margin of error 4 43 10 147 c) (4 pts) Construct a 94% confidence interval for the population mean. administrator would like to estimate the average GPA of all currently registered studen 21) (6pts) A college a random sample. He plans to estimate the average GPA to within 0.05 of the true population 5% confidence interval Assume the standard deviation of all GPA's in the student population is a 9 At least how many students does he need to includ- in the sample?Explanation / Answer
Result:
a).
df = n-1=41
critical value for t at 94% level =1.9343
b).
margin of error = t*sd/sqrt(n) = 1.9343*34/sqrt(42)
=10.1479
c).
lower limit = 645-10.1479 = 634.8521
upper limit = 645+10.1479 = 655.1479
94% CI = (634.8521, 655.1479)
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