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.