# physics

After 1.84 days, the activity of a sample of an unknown type radioactive material has decreased to 85.8% of the initial activity. What is the half-life of this material? (in days)

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1. Let T be the half life, in days.
(1/2)^(1.84/T) = 0.858
Take logs of both sides.
(1.84/T)*(-0.30103) = -0.06651
1.84/T = 0.22095
T = 8.33 days

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