The graph shows the number of gallons in a wading pool that is being drained. Using the points (1,160) and (3,80) as (x1,y1) and (x2,y2) , what is the rate of change in the number of gallons in the pool after each hour has passed?

40 gal./hr.
40 gal./hr.

−40 gal./hr.
negative 40 gal./hr.

140 gal./hr.
Start Fraction 1 over 40 End Fraction gal./hr.

−140 gal./hr.

1 answer

To find the rate of change, we need to calculate the difference in the number of gallons between the two points, and then divide it by the difference in time (hours) between the two points.

The initial number of gallons (y1) is 160, and after 3 hours, the number of gallons (y2) is 80.

The difference in y between the two points is 160 - 80 = 80 gallons, and the difference in x (time) is 3 - 1 = 2 hours.

Therefore, the rate of change in the number of gallons is 80 gallons / 2 hours = 40 gallons/hour.

So the correct answer is: 40 gallons/hour.