Answer:
d. 12:30 - 1:30 pm
Step-by-step explanation:
One way to work this is to plot the points on a graph and look for the segment with the greatest slope. That is the segment between 12:30 and 1:30 when the number of swimmers increased by 9 in one hour.
In the first interval (10:30 - 12:30), the number of swimmers increased by 10 in 2 hours, or an average of 5 per hour.
In the second interval (12:30 - 1:30), the number of swimmers increased by 9 in 1 hour, or 9 per hour.
In the third interval (1:30 - 3:30), the number of swimmers increased by 5 in 2 hours, or an average of 2.5 per hour.
In the last interval (3:30 - 5:30), the number of swimmers increased by 10 in 2 hours, or an average of 5 per hour.
The highest rate of increase is 9 per hour in the second interval, 12:30 to 1:30.