A tank was filled with 120 ℓ of water at 18 00. Water flowed out of the tank from 18 00 to 22 00. The line graph shows the amount of water in the tank from 18 00 to 22 00. Which one-hour period shows the most increase in the amount of water in the tank? Give your answer in this format. (Eg 12 00 to 13 00)


To find the most increase in a line graph, look for a decreasing slope that is the steepest. This indicates that the most decrease in the amount of water in the tank.

To prove:

Between 18 00 and 19 00:
Volume of water that flowed out
= 120 - 115
= 5 ℓ

Between 19 00 and 20 00:
Volume of water that flowed out
= 115 - 95
= 20 ℓ

Between 20 00 and 21 00:
Volume of water that flowed out
= 95 - 55
= 40 ℓ

Between 21 00 and 22 00:
Volume of water that flowed out
= 55 - 10
= 45 ℓ

One-hour period that shows the most decrease in the volume of water = 21 00 to 22 00 

Answer(s): 21 00 to 22 00