The following graph shows the decrease in the number of bacteria in a culture over time.

• A curve is shown on a coordinate grid.
• The horizontal axis is labeled Time (hours).
• The vertical axis is labeled Number of Bacteria.
• The curve begins near (0, 1700) and goes down and to the right.
• The curve decreases steeply then less steeply, passing through the points (1, 1400) and (3, 900).
• The curve straightens and exits the bottom right of the viewing window.

(a)What is the average rate of change of the number of bacteria in the culture between 1 and 3 hours after the measurements begin? bacteria per hour(b)Write a sentence that explains the meaning of the average rate of change in the context of this exercise.Because the average rate of change is ---Select--- positive negative , the bacteria population is decreasing at an average rate of bacteria per hour between 1 and 3 hours after measurements begin.