Beach Day by Rodger Bliss
June 2024

Water Cubes

Bonus unsolved riddle

originally published on April 25, 2011


The area of the floor of the tank is six square feet, and the water in it is nine inches deep. How much does the water rise if a one-foot metal cube is placed in it? How much further does the water rise if a second one-foot cube is also placed in the tank?


Please forward a RiddleDude email to friends and family in your address book. Suggest that they sign up for the daily email. Ask them to forward it to their friends. Paste us to your Facebook page!

You can best support our site—which is also YOUR site—by promoting it. is a free site and will always be a free site. We do it for the love of riddles. Remember, your comments and submissions are always welcome.


Submit your Guess




You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

6 guesses to Water Cubes

  • tashi

    9+12+12=33inch from the bottom the tank

  • Dude

    That’s not it. Check your math and keep trying.

  • Paul

    The water will rise from 9 inches to 10 and 1/2 inches after the first cube and up to 12 inches after the second cube.

  • Dude

    Close, but no.

    Keep trying.

  • nix

    after first: 10 4/5 inch.
    after second: 13 inch

  • Dude

    You nailed it, Nix!

    1.8 inches and then another 2.2 inches are the correct increases.

    Initially the volume of water is 6 * 9/12 = 4.5 cubic feet. The first cube effectively reduces the cross-sectional area of the tank to 5 square feet, causing the water to be 4.5/5 foot = 10.8 inches deep. Therefore rising 1.8 inches.

    The second cube is then placed on the floor of the tank, the cross-sectional area is 4 square feet up to a height of 1 foot, and this is filled by 4 cubic feet of water. The remaining 0.5 cubic foot, in a cross-sectional area of 6 square feet, requires a height of 0.5/6 foot = 1 inch. The water is therefore 13 inches deep and has risen by another 2.2 inches.

    You are today’s winner.