<PRE><B>Question 402769</B>
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</PRE>