Question: On October 7, 2010, the Wall Street Journal8 reported that Android cell phone users had increased to 10.9 million by the end of August 2010 from 866,000 a year earlier. During the same period, iPhone users increased to 13.5 million, up from 7.8 million a year earlier. Let A(t) be the number of Android users, in millions, at time t in years since the end of August 2009. Let P(t) be the number of iPhone users in millions.
(a) Estimate A'(0). Give units.
(b) Estimate P'(0). Give units.
(c) Using the tangent line approximation, when are the numbers of Android and iPhone users predicted to be the same?
(d) What assumptions did you make in part (c)?