Posted by **Jazmin** on Monday, May 30, 2011 at 8:52pm.

IF 80mg of a radioactive element decays to 10mg in 30 minutes, the half-life of this element is

a.10 min

b.20 min

c.30 min

d.40 min

the answer is a.10 min but i would like to know why, please help.

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