Question 1102063
t or T ?  Choose one but not both.

{{{N=330/(1+10(0.81)^t)}}}


You basically want to solve for t.  Once done, let N=80 and evaluate t.


{{{N/330=1/(1+10(0.81)^t)}}}

{{{330/N=1+10*0.81^t}}}

{{{10*0.81^t=330/N-1}}}

{{{N=80}}}----,------{{{10*0.81^t=25/8}}}

{{{0.81^t=25/80}}}

{{{0.81^t=5/16}}}

.

{{{t*log((0.81))=log((5/16))}}}

{{{t=log((5/16))/log((0.81))}}}

{{{t=0.50514/0.091514}}}

{{{highlight(t=5.5)}}}