A tank was filled with 190 ℓ of water at 09 00. Water flowed out of the tank from 09 00 to 13 00. The line graph shows the amount of water in the tank from 09 00 to 13 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 09 00 and 10 00:
Volume of water that flowed out
= 190 - 155
= 35 ℓ

Between 10 00 and 11 00:
Volume of water that flowed out
= 155 - 140
= 15 ℓ

Between 11 00 and 12 00:
Volume of water that flowed out
= 140 - 115
= 25 ℓ

Between 12 00 and 13 00:
Volume of water that flowed out
= 115 - 95
= 20 ℓ

One-hour period that shows the least decrease in the volume of water = 10 00 to 11 00 

Answer(s): 10 00 to 11 00