# SOLUTION: I would really appreciate some help with this one. The half life of a radio active substance is 125 days. How many days will it take for 82% of the substance to decay?

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 Question 402769: I would really appreciate some help with this one. The half life of a radio active substance is 125 days. How many days will it take for 82% of the substance to decay? Answer by scott8148(6628)   (Show Source): You can put this solution on YOUR website!At = Ao (1/2)^(t/h) ___ At is amount at time t ; Ao is initial amount ; t is the time ; h is the half life At / Ao = (1/2)^(t/h) 1 - .82 = (1/2)^(t/125) log(.18) = (t/125)log(1/2) [log(.18)] / [log(1/2)] = t / 125