Question

Suppose time taken to grade an exam-paper by an examiner has mean 13.1 min. and standard...

Suppose time taken to grade an exam-paper by an examiner has mean 13.1 min. and standard deviation 6.1 min. If the examiner has to grade 46 exam-papers, what is the approximate probability that she will finish grading in less than 648 min. (assuming grading times are independent and she grades continuously)? Answer to 4 decimal places.

14 refrigerators of a certain type has been returned to a distributor - 6 of these refrigerators have a defective compressor and 8 have less serious problems. A sample (without replacement) of 6 refrigerators are examined in random order, let X be the number of refrigerators with defective compressor among the examined ones. Answer all questions to 3 decimal places.

P(X = 3) =

错误. Tries 3/5 以前的尝试

P(1 < X ≤ 3) =

What is the expected number of refrigerators with defective compressor among the examined ones?

Tries 0/5

What is the standard deviation of number of refrigerators with defective compressor among the examined ones?

When circuit boards used in the manufacture of CD players are tested, the long-run percentage of defectives is 2%. A random sample of size n=29 of boards have been selected and checked.

What is the expected number of defective boards in the sample of 29? [Answer to 2 decimal places.] 0.58

The standard deviation of number of defective boards in the sample of 29 is: [Answer to 3 decimal places.] 0.754

What is the probability that at most 2 boards are defective in the sample? [Answer to 3 decimal places.] 0.980

The chance that the number of defective boards will exceed the mean by 2 standard deviation is: [Answer to 3 decimal places.]

错误. Tries 2/5 以前的
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Answer #1

1.)Suppose time taken to grade an exam-paper by an examiner has mean 13.1 min. and standard deviation 6.1 min. If the examiner has to grade 46 exam-papers, what is the approximate probability that she will finish grading in less than 648 min. (assuming grading times are independent and she grades continuously)? Answer to 4 decimal places.

Solution

Average()=648/46=14.09

approximate probability=0.8643

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