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13 October, 21:48

A potassium-40 sample starts with 50 atoms, and 1.25 billion years later, there are 25 atoms. What is the half life of potassium-40?

A. 25 years

B. 40 years

C. 1.25 years

D. 2.5 years

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Answers (1)
  1. 13 October, 21:54
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    Answer;

    Potassium-40 has a half life of 1.25 billion years.

    Explanation;

    New amount = Original amount * (1/2) ^n; where n is the number of half lives.

    Original amount is 50 atoms

    New amount is 25 atoms

    Therefore;

    25 = 50 * (1/2) ^n

    1/2 = (1/2) ^n

    Thus; n = 1

    n = 1 which is equivalent to 1.25 billion years

    Therefore;

    Potassium-40 has a half life of 1.25 billion years.
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