Question

In: Statistics and Probability

An automatic bottling machine fills oil into 2-liter (2,000 cm3) bottles. A consumer advocate wants to...

  1. An automatic bottling machine fills oil into 2-liter (2,000 cm3) bottles. A consumer advocate wants to test the null hypothesis that the average amount filled by the machine into a bottle is at least 2,000 cm3. A random sample of 40 bottles coming out of the machine was selected and the exact contents of the selected bottles are recorded. The sample mean was 1,999.6 cm 3. The population standard deviation is known from past experience to be 1.30 cm3.
  1. Test the null hypothesis at α of 5%.
  2. Assume that the population is normally distributed with the same standard deviation of 1.30 cm3. Assume that the sample size is only 20 but the sample mean is the same 1,999.6 cm3. Conduct the test once again at α of 5%.
  3. If there is a difference in the two test results, explain the reason for the difference

Solutions

Expert Solution

(a)

(b)

(c)

Yes, in part a we reject the null hypothesis while in part b we fail to reject the null hypothesis.

Reason: As the sample size decreases standard error increase and test statistics decreases. So chances to reject the null hypothesis also decreases.


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