Radium-221 has a half-life of 30 seconds. How long will it take for 77% of a sample to decay?
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Originally Posted by cheer4life1694 Radium-221 has a half-life of 30 seconds. How long will it take for 77% of a sample to decay? y = fraction of substance left after time t h = half-life in same units as t $\displaystyle y = \left(\frac{1}{2}\right)^{\frac{t}{h}}$
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