Question

In the second question of the 2nd lecture's problem it states "you can check your answer by checking f(11)=$175 and f(10)=$220", how is that determined? (besides making a whole graph, or is that what is meant?)

Answer 1

You're given this formula:\[f(t)=-5t+60t+120\]When you calculate f'(10) you get -40. To check whether this result seems reasonable you can plug 10 and 11 into the original formula and see that over that increment f(t) actually does decline by about $40.

Answer 2

Thank you for helping me. :)