Question

A colony of bacteria is growing exponentially according to the function below, where t is in hours. About how many hours will it take for the population to reach 400?

Answer 1

The function is:
B ( t ) = 4 * e^(0.8 t)
4 * e^(0.8 t) = 400
e^(0.8 t) = 400: 4
e^(0.8 t) = 100   / ln
ln e^(0.8 t) = ln 100  ( and since: ln e = 1 and ln e^x = x * ln e )
0.8 t = 4.6
t = 4.6 : 0.8 = 5.76 ≈ 6
Answer:
D ) 6 hours.