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Fifteen

Practice addition by trying to take three cards that add to 15 before your opponent can.

Ages: 5+
Players: 2
Time: Under 10 Minutes
Type: number games
Location: tabletop
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Ages: 5+
Players: 2
Time: Under 10 Minutes
Type: number games
Location: tabletop

Instructions

Pull out Ace through 9 of a single suit from a standard deck of cards, and lay them out between players. (Or, use the numerals 1-9 from your Number Deck.)

Playing cards ace through nine layed out in a row

Now players take turns choosing 1 card at a time from the cards in the middle. The winner is the first to collect 3 cards that add to 15.

Cards after some have been taken by players
The three cards on the left show a winning trio: 3 + 7 + 5 = 15.

If your first 3 cards don't add to 15, it doesn't mean you've lost. You can still win by choosing another card that, when combined with any two of your cards, adds to 15.

As you play, you'll notice that a big part of the game is trying to block your opponent. Think about what cards they have, and what they still need to get a sum of 15. If you can, take that card before they do!

Don't forget: it's Beast Academy Playground, not Beast Academy Study Hall. Change the rules, be silly, make mistakes, and try again. The Variations and Learning Notes are here for you if you want to dive deeper, but not all of them apply to learners of every age. The most important thing is to have fun.

Variations d

Magic Squares:

A classic math puzzle. Try to arrange your cards (1-9) into a 3x3 grid, so that every row, every column, and both diagonals all add to the same number. Can kids figure out what that number has to be even before solving the Magic Square? (Hints in the title of this game, and below in Learning Notes.)

Classroom Tips d

This is a great one for classroom use because of the surprising tie-in to magic squares (see Variations below). Play to practice addition and strategic thinking.

Discussion Questions

  • Which cards are easier to use to get to 15?
  • Which cards are harder to use to get to 15?
  • Can you make 15 with all odd numbers?
  • Can you make 15 with all even numbers?
  • Is it better to block your opponent or to focus on making 15 to win?

Alignment with Beast Academy Curriculum

  • Level 2, Chapter 8: Strategies (+ & -)

See Variations and Learning Notes for more ideas on how to adapt this activity and incorporate it into your classroom.

Learning Notes d

Magic Squares:

See the variation above for instructions on making a Magic Square. Children will likely need some assistance. Help them break down the challenge into parts:

First, guide them in figuring out what the "magic sum" should be (that is, what each row, column, and diagonal should add up to). Ask what the sum of all 9 cards is. This is a great chance to be clever about adding up numbers. Look for pairs that add to 10 first: 1 + 9, 2 + 8, 3 + 7, and 4 + 6. These add to 40, with the 5 still uncounted. So the sum is 45. Since the sum of each of the three rows has to be the same, we know that each row must be a third of 45, or 15. We've found our magic number.

Second, ask the child to form 3 rows that each add to 15. For this step, ignore columns and diagonals. This can be tough, depending on the age and ability of the child. But it's good addition practice, and good practice in number sense ("If this row is too big, I need to switch out one number with a smaller number.").

Third, now that there are 3 rows that each add to 15, challenge your child to rearrange the cards so that each column also equals 15. They can do this by switching numbers within a row. This keeps the sum of each row the same.

Fourth, try to get the diagonals to equal 15. This part is the toughest. The trick is to realize that you can move a whole column to another position, or a whole row. Let your child try this for a bit. When it's done, the Magic Square should have the 5 in the center. Here's one possible arrangement (though there are more):

Three by three magic square grid with the numbers, from top left to bottom right, 8 1 6 3 5 7 4 9 2

Remember grouping all the pairs that add to 10 earlier? Those pairs are all hiding in this square on either side of the 5. The 1 and 9 are on opposite squares on either side of the 5. So are the 2 and 8, 3 and 7, and 4 and 6!

Tic-Tac-Toe:

Once you've made your Magic Square, copy it onto a piece of paper. Then play a few games of Fifteen again. This time, as you play, keep track of which cards each player chooses by marking an X for one player, and an O for the other player on the Magic Square. It won't take long for your child to recognize that playing Fifteen is just the same as playing Tic-Tac-Toe on a Magic Square! (This is why Fifteen so often ends in a draw, just like Tic-Tac-Toe.)

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Materials
  • standard deck of cards
Learning Goals
  • addition
  • strategic thinking
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Image of Ms. Q

Ready to level up?

Keep problem solving with Beast Academy’s full math curriculum for students ages 7–13. Check out our captivating comic book series and immersive online platform.

LEARN MORE

Bring problem-solving to your classroom

Keep your entire class engaged with a full book and online math curriculum, for students ages 7–13. 98% of teachers say they’re satisfied with Beast Academy.

LEARN MORE
Image of a BA book