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If 57 mg of radium 221 has a half life of 30 seconds. How long will it take for 95 percent of the sample to decompose?
JulieVu
try using my formula....
ar=a(1/2)^2t
therefore, 57(.05) = 57(1/2)^2t
and 57s cancels out, .05 = 1/2^2t
log .05 = log .5^2t
divide log .5 from both sides,
4.32 = 2t
t = 2.16, therefore 126 seconds or 2 minutes and 6 seconds
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