- (a) Use the Trapezoid Rule, with h = 60 min:
(b) Draw a horizontal line at y = 20 (as shown on the graph below), representing the rate at which
letters are processed then.
(i) Letters began to pile up when they arrived at a rate greater than that at which they were being
processed, that is, at t = 10 A.M.
(ii) The pile was largest when the letters stopped piling up, at t = 2 P.M.
(iii) The number of letters in the pile is represented by the area of the small trapezoid above the
horizontal line:
(iv) The pile began to diminish after 2 P.M., when letters were processed at a rate faster than they
arrived, and vanished when the area of the shaded triangle represented 1500 letters. At 5 P.M.
this area is letters, so the pile vanished shortly after 5 P.M.
