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# Confidence Internval, Normal Probability&Hypothesis Testing

#4. you collected the following information:

n=38

x bar= 12.35

s=3.82

find the 95% confidence interval estimate for m- mule

#2. heavy duty light bulbs made by a certain company claim to have lives that are normally distributed with a mean of 5000 hours and a standard deviation of 400 hours.

A. find the probability that one of these light bulbs lasts more than 6000 hours.

B. in a box of 1000 such light bulbs, how many do you expect will last between 4900 and 5512 hours?

C.what is the 94th percentile of this distribution?

#3 .you sampled 500 BobBob GPS units and found that percisley 20 had some defect. the rest were free of defect.

A.find a 90% confidence interval estimate of the true proportion of defective BobBob GPS units. what is the margin of error in your estimate?

B.the BobBob company has claimed that less than 1% of all its units are defective. is this consistent with expectations? why or why not?

#5. given the hypothesis test
ho: p= 0.8
h1: p< 0.8
in a sample of 200 you pulled 148 successes and 52 failures. what is the result of this hypothesis test at the (a) a=0.05 (b) a=0.01 level?

#6. the power company claims that it delivers 125 volts a day to Triola's house. to test this claim. Triola sets up his own device which measures the voltage to his home. on 40 such days, he measured the voltage to his house. On these 40 days the mean voltage was 123,7 volts with a standard deviation of 0.24 volts.

B. at the a=0.01 level, test the claim that the average daily voltage is different than 125 volts.

#### Solution Summary

The solution provides step by step method for the calculation of testing of hypothesis, normal probability and confidence interval. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.

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