the mean life a digital clock is 305 days. The lives of the batteries follow the normal distribution.The battery was recently modified .To last longer.A sample of 20 of the modified batteries had a mean life of 311 days ?With the standard deviation 12 days ?Did the modification increase the mean life of the battery ?
1) state the null hypothesis and the alternative hypothesis .
2) show the decision rule graphically .Use the 0.05 significance level!
3)compute the value if T.what is your decision regarding null hypothesis ?
Answer in brief?
Answers
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From past records it is known that the average life of a battery used in a digital clock is 305 days. The battery life is normally distributed. The battery was recently modified to last longer.
Ho: u = 305
Ha: u > 305
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A sample of 20 of the modified batteries was tested. It was discovered that the mean life was 311 days and the sample standard deviation was 12 days.
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We want to test at the 0.05 level of significance whether the modification increases the life of the battery. What is our decision rule?
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Critical value for df=19 and alpha =5%: t = 1.729
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Reject Ho if the test statistic is greater than 1.729
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