calculus

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How do I set-up/solve this problem? Please help me.

The half-life of the radioactive isotope gallium-70 is 20 minutes. If the initial amount of gallium-70 is 25 milligrams, when will 10 milligrams be left?

  • calculus -

    can you solve

    10 = 25(.5)^(t/20) where t will be in minutes ?

  • calculus -

    This is what I got..

    25(1/2)^(t/20)=10
    (1/2)^(t/20)=10/25=2/5

    (1/2)^(t/20)=2/5
    t/20=log(2/5)/log(1/2)
    t=20(log(2/5)/log(1/2))
    t=26.44

    Is this correct?

  • calculus -

    correct, good job.

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