Take a cylinder with a 50-centimeter radius that is 100 centimeters
tall. Begin pouring water in. During the first three minutes, pour one
liter per minute [recall that a liter is 1000 cubic centimeters]. During
the second three-minute period, pour two liters per minute; during the
third three-minute period, pour three liters per minute, and so forth.
After 50 minutes, how deep will the water be?
How long will it take to fill the cylinder?
Source: An entrance exam for Azabu Junior High School in Tokyo