Students participating in a psychology experiment attended several lectures and were given an exam. Every month for the next year, the students were retested to see how much of the material they remembered. The average score for the group are given by the human memory model

f(t) = 90 - 15 log (t + 1) ,0 t 12

where t is the time in months.

a)Use a graphing calculator to graph the function over the specified domain.

b)What is the average score on the original exam (t = 0)?

c)What was the average score after 6 months?

d)What was the average score after 12 months?

e)When did the average score decrease to 75?