# Pre Calculus

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Exponential growth and decay

find the half life of a radioactive substance if 220 grams of the substance decays to 200 grams in 4 years?

• Pre Calculus -

Let the half life be T years

2^(-4/T) = 200/220 = 0.9091
(-4/T) log 2 = log 0.9091
-4/T = -0.1375
T = 29.1 years

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