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15 August, 09:15

Benny wants to estimate the mean lifetime of Energizer batteries, with a confidence level of 97%, and with a margin of error not exceeding ±10 hours. If the standard deviation of the lifetime is known to be 55 hours, how many batteries does Benny need to sample?

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  1. 15 August, 11:48
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    143 batteries does Benny need to sample

    Explanation:

    Given data

    confidence level = 97%

    error = ±10 hours

    standard deviation SD = 55 hours

    to find out

    how many batteries does Benny need to sample

    solution

    confidence level is 97%

    so a will be 1 - 0.97 = 0.03

    the value of Z will be for a 0.03 is 2.17 from standard table

    so now we calculate no of sample i. e

    no of sample = (Z * SD / error) ²

    no of sample = (2.16 * 55 / 10) ²

    no of sample = 142.44

    so 143 batteries does Benny need to sample
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