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7 January, 16:55

The amount of a radioactive substance decreases by 10% every

12 hours. Currently the amount of substance is 100 grams. If n is

a whole number, which expression represents the number of

grams of substance left n days from now?

A. 100 (0.81) ^n

B. 100 (1.1) ^2n

C. 100 (0.81) ^n/2

D. 100 (0.8) ^n

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Answers (1)
  1. 7 January, 17:19
    0
    Step-by-step explanation:

    We would apply the formula,

    y = ab^t

    Where

    a represents the initial amount of substance.

    t represents the decay time.

    From the information given

    a = 100

    t = 12 hours

    Since after 12 hours, the amount of substance reduces by 0.1, then

    y = 0.1 * 100 = 10

    Therefore

    10 = 100 * b^12

    Dividing through by 100, it becomes

    0.1 = b^12

    Raising both sides of the equation by 1/12, it becomes

    0.1^ (1/12) = b^12/12

    b = 0.8

    The equation becomes

    y = 100 (0.8) ^t

    Where t = n, the expression becomes

    y = 100 (0.8) ^n
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