A Rumor Begins to Spread Across a College Campus $D = \frac { \ln 2 } { r / 7 }$

Multiple Choice

A rumor begins to spread across a college campus. The amount of time in days that it takesthe number of people that have heard it to double is given by $D = \frac { \ln 2 } { r / 7 }$ where r is the rate of the spread of the rumor per week. If a particular rumor is spreading at a rate of 28% per week, how long is the doubling time? Round to the nearest tenth of a day.

A) 2.5 days
B) 3.9 days
C) 17.3 days
D) 13.9 days