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# Normal Probability: Life span of bulbs & Cut off mark

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1). In an examination the mean score was 80, the standard deviation was 10, and the grades followed a normal distribution. The instructor wants to assign A's to the top 12%. Where should the cutoff point for A's be?

(2). A company manufactures electric light bulbs that have an average life of 1000 hours and a standard deviation of 50 hours. Find the probability that a bulb selected at random will have a life span of between 900 and 950 hours.

##### Solution Summary

The solution provides step by step method for the calculation of probability using the Z score. Formula for the calculation and Interpretations of the results are also included. The life span of bulbs and cut off marks are examined.

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Statistic
1). In an examination the mean score was 80, the standard deviation was 10, and the grades followed a normal distribution. The instructor wants to assign A's to the top 12%. Where should the cut off point for A's be?
Let x be the scores obtained in the examination. Given that X is normal with mean µ = 80 and standard ...

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