Party 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.

Party Fish

December 11, 2018

It’s fun to get a party favor after a birthday party. Well, imagine if that favor was a live fish. That happened here at Bedtime Math: at a friend’s party, every one of the 32 kids took home a plastic bag of water with a confused fish swimming inside. Of course, each fish then needed the right set-up in its new home: a fishbowl or aquarium, a layer of colorful gravel (little stones), and then a cute castle or seashells for decoration…maybe even a few fish friends. Fishbowls also need the right amount of water: the rough rule is “1 gallon per inch of fish” when lined up end to end. We hope all 32 fish like their new homes!

Wee ones: If after the party you get a fish and 3 seashells, what numbers do you say to count your party favors?

Little kids: If you have 2 pet goldfish that are each 3 inches long, how many total inches long are they together?  Bonus: If they were each 5 inches long, would 9 gallons of water be enough? (Remember, you need 1 gallon per total inch…)

Big kids: If 13 of the 32 fish got a new fish buddy once home, how many total fish do the partygoers have now?  Bonus: If every 5th fish owner (starting with the 5th) bought a castle, how many castles did the store sell?

The sky’s the limit: The rule for giving fish water is 1 gallon per inch of fish. If your local pet store sells 2-inch and 5-inch tropical fish, and your fishtank can hold 20 gallons, how many different combos of fish would use exactly the full 20?












Wee ones: 1, 2, 3, 4.

Little kids: 6 inches.  Bonus: Not quite, since they would need 10 gallons.

Big kids: 45 fish.  Bonus: 6 castles, for the 5th, 10th, 15th, 20th, 25th, and 30th fish owners.

The sky’s the limit: Just 3 different combos: 10 small fish, 2 big fish and 5 small, and 4 big fish. We can’t have 1 big fish or 3 big fish, because they’d require an odd number of gallons, leaving an odd number that can’t be filled by 2s.

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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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