A company designs an app that brings in 200 new users daily. On average, active users will abandon the app after 15 days. With the SIR model, use I(t) to represent the number of active users at time t days, and use R(t) to represent the number of active users that abandon the app at time t days.

i. What is the rate equation for R’(t)? For I’(t)? Explain.

ii. If at one time there are 700 active users, would the number of actives be increasing or decreasing and why? What if there were 2000 actives?85