Overload of Pet Fish

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Overload of Pet Fish

July 17, 2014

No matter how much you love pet fish, there’s a limit as to how many you can have. The rule is that you need about 1 gallon of water for every inch of fish, since they need enough oxygen to “breathe” for themselves from the water, and they need room to swim without bumping into each other all the time…and since fish poop right in the water where they swim, you don’t want too much of that in one small space, either. So even a glass tank might hold only a dozen fish. Well, a Wisconsin guy named Bill Wann decided he wanted lots of pet fish, so he built his own enormous home fish tank. It’s 24 feet long, 10 feet wide and 10 feet tall; in fact, the tank is so huge that he had to build it first before building the rest of the house around it! With 20,000 gallons of water, 2,000 pounds of sand and 20,000 pounds of rocks, it’s the largest home aquarium in North America, and home to 160 happy fish. We just wonder how he remembers all their names.

Wee ones: Which is longer, a 2-inch tang or a 6-inch clownfish?

Little kids: The aquarium’s windows are 10 feet tall and 6 feet wide, and took 11 people to lift just one! If you and Mr. Wann lift a window together, how many other people would have to help you?  Bonus: If 1 of Mr. Wann’s 160 fish gets eaten by another fish (which hopefully never happens…), how many fish are left?

Big kids: A gallon of water can support 1 total inch of fish, meaning 2 gallons can support either a 2-inch fish or two 1-inch fish. If all of Mr. Wann’s fish are 2 inches long, how many fish can his 20,000 gallons support?  Bonus: The tank is 24 feet wide, 10 feet long and 10 feet tall. How many cubic feet of water does it hold? (Reminder: The length x width x height of a box gives you its volume, or the amount of space inside it.)

The sky’s the limit: If Mr. Wann wants some 1-inch goldfish, some colorful 2-inch tangs, and some 6-inch clownfish like Nemo, how many of each can his 20,000-gallon tank support if he wants equal numbers of tangs and clownfish and twice as many goldfish as tangs?




Wee ones: The 6-inch clownfish.

Little kids: 9 other people.  Bonus: 159 fish left.

Big kids: 10,000 fish.  Bonus: 2,400 cubic feet.

The sky’s the limit: If he has the same number of tangs and clownfish but double the goldfish, then one full “set” of fish will add 10 inches of fish (2 inches of goldfish, 2 inches of tang, 6 inches of clown). The 20,000 gallons support 20,000 inches, or 2,000 of these sets of 2 goldfish, 1 tang and 1 clownfish. So there can be up to 4,000 goldfish, 2,000 tangs and 2,000 clownfish.

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About the Author

Laura Overdeck

Laura Overdeck

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.

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