Question 1140195
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<s>A=A0e−0.0048t</s> {{{A=A[o]e^(-0.0048t)}}}, where A0 is the initial amount and t is the time in years.  If A0=580 grams, find the time for the radioactive substance to decay to 405 grams.
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{{{ln(A)=ln(A[o])+ln(e^(-0.0048t))}}}

{{{ln(A)=ln(A[o])-0.0048t}}}

{{{ln(A)-ln(A[o])=-0.0048t}}}

{{{ln(A[o])-ln(A)=0.0048t}}}

{{{t=(ln(A)-ln(A[o]))/0.0048}}}
This is as a formula.  You substitute the given values and evaluate.