A tank was filled with 130 ℓ of water at 13 00. Water flowed out of the tank from 13 00 to 17 00. The line graph shows the amount of water in the tank from 13 00 to 17 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 13 00 and 14 00:
Volume of water that flowed out
= 130 - 85
= 45 ℓ

Between 14 00 and 15 00:
Volume of water that flowed out
= 85 - 75
= 10 ℓ

Between 15 00 and 16 00:
Volume of water that flowed out
= 75 - 55
= 20 ℓ

Between 16 00 and 17 00:
Volume of water that flowed out
= 55 - 30
= 25 ℓ

One-hour period that shows the least decrease in the volume of water = 14 00 to 15 00 

Answer(s): 14 00 to 15 00