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In the Triangle Sums Puzzle, you are challenged to arrange the numbers 1 to 9 in the squares so that the sum of the numbers in each pair of squares is the same as the number in the triangle that touches both squares in the pair. You may only put one number in each square, and you may use each number only once.

I found the Triangle Sums Puzzle in The Little Giant Encyclopedia of Puzzles by The Diagram Group. I am always on the lookout for new puzzles that I can use with my students from pretty much any puzzle book I can get my hands on.

I printed the triangle sums puzzle on 11 x 17 cardstock. Then I printed the numbers 1 through 9 on colored paper which I laminated and cut apart. I have also uploaded an 8.5 x 11 inch version if you don’t have the ability to print on larger paper sizes. I print on 11 x 17 at school by using the bypass tray on my school’s copy machine. This size of paper makes the perfect size for students to work on in small groups.

I find it is much easier for students to not use a number more than once if they have movable pieces.

Here’s a partial (but incorrect) solution. 5+4=9. 4+8=12. 8+3=11. 3+6=9. The next number would be 2 since 6+2=8. However, the 2 needs a 4 to sum to 6, but 4 has already been used.

Have fun puzzling with this puzzle on your own or with your students!