Answer: 80 pages per day.
Step-by-step explanation: To find the average rate of change in the number of pages read per day from day 3 to day 5, we need to calculate the slope using the formula m = (Y2 - Y1) / (X2 - X1).
In this case, X1 is day 3, X2 is day 5, Y1 is the number of pages read on day 3, and Y2 is the number of pages read on day 5.
From the table, we can see that on day 3, Gladys read 71 pages, and on day 5, she read 231 pages.
Plugging these values into the slope formula, we get:
m = (231 - 71) / (5 - 3) = 160 / 2 = 80
Therefore, the average rate of change in the number of pages read per day from day 3 to day 5 is 80 pages per day.