They were shared in THINK ABOUT IT! Mathematics Problems of the Day which was published by Creative Publications in 1982.
The book is out of print and very hard to find copies of online.
In the Sum to Twenty-One Puzzle, students are given a 4 x 4 grid that already has six numbers filled in. Their task is to place the numbers 0-9 in the grid so that each row, diagonal, and column sums to 21.
If you like this magic square style puzzle, I also recommend checking out the Big Magic Puzzle.
Interested in even more puzzles? Check out my puzzles page!
Free Download of Sum to Twenty-One Puzzle
I have created a printable PDF version of this puzzle. If you would like to edit it, I have uploaded the editable Publisher version. Since we’re currently in the middle of a pandemic, I have also created some digital versions which I will share below.
Digital Version of Sum to Twenty-One Puzzle
I created a Google Slides version of this activity.
I intentionally do not make answers to the printable math puzzles I share on my blog available online because I strive to provide learning experiences for my students that are non-google-able. I would like other teachers to be able to use these puzzles in their classrooms as well without the solutions being easily found on the Internet.
However, I do recognize that us teachers are busy people and sometimes need to quickly reference an answer key to see if a student has solved a puzzle correctly or to see if they have interpreted the instructions properly.
If you are a teacher who is using these puzzles in your classroom, please send me an email at email@example.com with information about what you teach and where you teach. I will be happy to forward an answer key to you.