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MathBait™ Multiplication

Secret Codes

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This fun game can be played as a quick warm-up or a long-form game as needed. The leader selects a secret code and organizes their bones. Providing limited information they challenge the class to determine their code. Excellent for building problem solving and deep thinking as well as building fluency with multiplication, Secret Codes will make you forget you are in math class!


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Playing with Napier's Bones







This activity is great for students just learning multiplication or working on fluency practice. It can be a quick warm up or a long-form game over multiple rounds.

In this game, students make observations about numbers and multiples to help determine the secret code.

Boy holding a paper with Napier's Bones partially filled out.

Grab a set of empty rods and display them for the class to see. You can find a printable version in MathBait™ Multiplication Part 5.

Next, select a leader (this can be a teacher or student). Using a completed half-set of bones (one bone for each digit), in secret the leader will rearrange the bones in any order to create their Secret Code.

For instance, a code may be 5093627418. One of every bone is used exactly one time. For older or advanced students, the game can be played at a higher level of difficulty by allowing a full set of 20 bones (2 of each digit). This allows some digits to be used more than once and other digits not at all, such as the code 5613486325.

Each round, the leader will select a value to enter into the bones. They should display their value and its placement for all to see by adding to the empty set. If pressed for time, the leader may write out all ten clues at once.

For a super quick game, have the leader place one value on each bone, including tens and ones. Students use reasoning to determine the code. For instance, a 15 in the third row tells us 3× this number =15. Students will determine the value must be 5.

If you have more time, or more advanced learners, have the leader place only a single value (a ten or a one) in each column.

The remaining players have the chance to guess the Secret Code.

This game is great for both the leader and the players. In the image above, note the 7 in the ones place of the fourth rod. The only value on our table such that 9×? contains a 7 in the ones place is 9×3, so the fourth rod must be a 3. The leader must think critically about what clues they will give.

The criteria to win the game depends on your variation. It can simply be a fun activity without points to get the class started. If making Secret Code a regular activity, consider giving the leader a point if they stump their classmates. Have a special place in the classroom to display the current high score. Another alternative is simply the first person to guess the secret code wins.

Secret Codes not only helps students to become more familiar with multiples, it also encourages students to look for patterns within the bones or the multiplication table. Students develop reasoning and problem-solving skills as they play. In the board above, the 6 on the final bone tells students we are looking for a multiple of 2 with a 6 in the ones place. This could be 6 or 16. Both the leader and students must consider how to pick and interpret clues in order win.

The material on this page is copyrighted by MathBait™. Please use and enjoy it! MathBait™ provides a temporary license for Non-Commercial purposes. You are not permitted to copy, distribute, sell, or make derivative work without written permission from MathBait™. 

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