question
You are given a 3-quart bucket, a 5-quart bucket, and an unlimited supply of water. How can you measure out exactly 4 quarts?
Drawing a simple graphic may help.
Start by filling the 5-quart bucket completely. Use the 5-quart bucket to fill the 3-quart bucket - leaving 2 quarts in the 5-quart bucket. Empty the 3-quart bucket and fill it with the 2 quarts from the 5-quart bucket. Fill the 5-quart bucket. Fill the 3-quart bucket (which already has 2 quarts) using the 5-quart bucket. This leaves exactly 4 quarts in the 5-quart bucket.