# math

posted by Rachel

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent.
a)(a) What is the half-life of the element? half-life:
b)How long will it take for a sample of 100 mg to decay to 51 mg?
time needed:

1. Steve

.36 = (1/2)^(100/k)
k = 67.84

so, the half-life is 67.84 days
Makes sense, since the sample has decreased by a little more than 1/2 in 100 days.

51/100 = (1/2)^(t/67.84)
t = 65.9 days

2. Jack

GREETINGS

3. dygae

no

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