A tank was filled with 120 ℓ of water at 15 00. Water flowed out of the tank from 15 00 to 19 00. The line graph shows the amount of water in the tank from 15 00 to 19 00. Which one-hour period shows the least decrease in the amount of water in the tank? Give your answer in this format. (Eg 12 00 to 13 00)


To find the least decrease in a line graph, look for a decreasing slope that is closer to zero or nearly flat. This indicates that the least decrease in the amount of water in the tank.

To show:

Between 15 00 and 16 00:
Volume of water that flowed out
= 120 - 105
= 15 ℓ

Between 16 00 and 17 00:
Volume of water that flowed out
= 105 - 100
= 5 ℓ

Between 17 00 and 18 00:
Volume of water that flowed out
= 100 - 70
= 30 ℓ

Between 18 00 and 19 00:
Volume of water that flowed out
= 70 - 25
= 45 ℓ

One-hour period that shows the least decrease in the volume of water = 16 00 to 17 00 

Answer(s): 16 00 to 17 00