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Author:
david utsey

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1.A television picture tube of manufacturer A has a mean lifetime of 6.5 years a standard deviation of 0.9 years, while those of manufacturer B has a mean lifetime of 6.o years and a standard deviation of 0.8 years.

What is the possibility that a random sample of 36 tubes from manufacture a will have a mean lifetime that is at least 1 year more than the mean lifetime of a sample of 49 tube from manufacture B.

2.An electrical firm manufactures lightbulbs that have a length life that is approximately normally distributed, with mean equals to 8 hours and a standard deviation 40 hours. Find the probability that random sample of 16 bulbs that will have an average life of less than 775hours.

(2) Chemical engineer claims that the population may yield of certain batch process is 500gms per millimeter of raw material. To check this claims, he sample 25 batches of these month. If the computed t- values falls between –t0.05 and t 0.05, he is satisfied with these claims. What conclusion should he draw from a sample that has a mean = 5.8 grams per millimeter and a sample standard deviation S=40 grams? assume the distribution of yields to be approximately normal.

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