T(d) is a function that relates the number of tickets sold for a movie to the number of days since the movie was released. The average rate of change in T(d) for the interval d = 4 and d = 10 is 0. Which statement must be true?

The average rate of change from day 4 to day 10 is [T(10) − T(4)] ÷ (10 − 4). Since it equals 0 and the days are six days apart, T(10) − T(4) must be 0. Therefore, the number of tickets sold was the same on the fourth and tenth days; this does not mean that no tickets were sold.

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