It’s fun to get a party favor after a birthday party, but imagine if that favor was a live fish. That happened here at Bedtime Math: at a friend’s party, 32 kids each 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. An aquarium needs 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?
Answers:
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.
