Statistics

An accelerated life test on a large number of type-D alkaline batteries revealed that the mean life for a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal distribution. The standard deviation of the distribution was 1.2 hours. About 95.44% of the batteries failed between what two values?
8.9 and 18.9
12.2 and 14.2
14.1 and 22.1
16.6 and 21.4

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  1. 99.44% = mean ± 1.99 SD

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  2. 17

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  3. An accelerated life test on a large number of type-D alkaline batteries revealed that the mean life for a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal distribution. The standard deviation of the distribution was 1.2 hours. About 95.44% of the batteries failed between what two values?
    Selected Answer:
    Correct 16.6 and 21.4
    16.6 and 21.4
    14.1 and 22.1
    8.9 and 18.9
    12.2 and 14.2

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  4. Ball-Bearings, Inc. produces ball bearings automatically on a Kronar BBX machine. For one of the ball bearings, the mean diameter is set at 20.00 mm (millimeters). The standard deviation of the production over a long period of time was computed to be 0.150 mm. What percent of the ball bearings will have diameters of 20.27 mm or more?
    Selected Answer:
    Answers:
    12.62%
    3.59%
    41.00%
    85.00%

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  5. 53. The mean score of a college entrance test is 500; the standard deviation is 75. The scores are normally distributed. What percent of the students scored below 320?
    A) About 50.82%
    B) About 34.13%
    C) About 7.86%
    D) About 0.82%

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  6. the averages starting salary of individuals with a master's degree in statistics is normally distributed with a mean of $48,000 and a standard deviation of $6,000. What is the probability that a randomly selected individual with a master's in statistics will get a starting salary of at least $55,500?

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