Question 1113350
20 minutes is 1/3 hour.
t(1/3)=100*(0.727)^(1/3)=100*0.8992=89.92 or 90 minutes
50=100*0.727^t
0.5=0.727^t
ln both sides
-0.693=t ln (0.727)
t=-0.6931/-0.3188
=2.17 hours or 2 hours 10  minutes