can help me with this question :S?(adsbygoogle = window.adsbygoogle || []).push({});

If 70% of a radioactive substance remains after one year, find its half-life.

and

Strontium-90 is a radioactive isotope with a half-life of 29 years. If you begin with a sample of 800 units, how long will it take for the amount of radioactivity of the strontium sample to be reduced to

(a) 400 units

(b) 200 units

(c) 1 unit

*it has to do wit exponential growth and decay and maybe... with differential equations

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# Homework Help: Half life :s

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