A student makes 10 one-second measurements
    of the disintegration of a sample of a long-lived
    radioactive isotope and obtains the following
    values.

                3, 0, 2, 1, 2, 4, 0, 1, 2, 5

    How long should the student count to establish
    the rate to an uncertainty of 1 percent?

    (A)    80 s
    (B)   160 s
    (C) 2,000 s
    (D) 5,000 s
    (E) 6,400 s


    這題是GRE subject的考題，我對這題完全沒有概念，
    不知道從何著手。請各位幫忙一下。也希望能夠指導
    我該看哪些主題，或著是看哪些書。

    謝謝大家了。



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