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8-129.
A 100 gram sample of a radioactive isotope is taken from a protective container. After four hours the sample decays to 85 grams. What is the half-life of the substance? Homework Help ✎
Substitute the initial amount 100 for 'a'. Substitute 85 for 'y' and 4 for 't'.
Solve for k.
Since we want to find how long it takes for half to decay, solve: 1 = 2e−0.0406t
This indicates an amount of 2 was reduced to 1.
y = aekt
85 = 100e4k
k = −0.0406
t = 17.06 hours