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An unknown radioactive element decays into non-radioactive substances. In 860 days the radioactivity of a sample...

An unknown radioactive element decays into non-radioactive substances. In 860 days the radioactivity of a sample decreases by 49 percent.

(a) What is the half-life of the element?
half-life:   (days)

b) How long will it take for a sample of 100 mg to decay to 78 mg?
time needed:  (days)

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