math
posted by julie .
A company begins a radio advertising campaign in Chicago to market a new soft drink. The percentage of the target market that buys a soft drink is estimated by the function f(t)=100(1e^0.01t), where t is the number of days of the campaign. After how long will 80% of the target market have bought the soft drink?

.8 = 1  e^.01t
.2 = e^.01 t
ln .2 = .01 t
t = (ln .2)/.01 = 161