Question 1192688
{{{y=A(1/2)^(x/5730)}}}; initial amount, A, final amount, y, time in years x.


{{{(1/2)^(x/5730)=y/A}}}

{{{log(((1/2)^(x/5730)))=log((y/A))}}}

{{{(x/5730)log((1/2))=log((y/A))}}}

{{{x=5730*log((y/A))/log((1/2))}}}

Lost 85% means kept 15% as remaining

{{{x=5730*log((0.15))/log((1/2))}}}{{{substitutions_of_values}}}
{{{ x=15682}}}

{{{highlight(x=15700)}}}  {{{best keep three significant figures}}}


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{{{y=Ae^(-0.00012097x)}}}

{{{0.15=e^(-0.00012097x)}}}

{{{ln(0.15)=-0.00012097x}}}

{{{x=-ln(0.15)/0.00012097}}}

{{{x=15682}}}

{{{highlight(x=15700)}}}