Earlier today I set you six puzzles that use a square piece of paper, in the light of new research saying that the best way to improve maths performance is to train ‘spatial reasoning’ using physical objects.
1. The triangle fold
Fold a square paper in such a way that fold lines (and possibly an edge) mark an equilateral triangle. (Compass and ruler not allowed!)
Solution Here is one way, that uses the side length of the square as the side length of the triangle.
It is possible to fold a larger equilateral triangle – I’ll leave that as an exercise for the reader. Clue: the tip of the triangle is still a corner of the square, but the sides are folded at 15 degrees from the sides of the square.
2. The 3D shape
Can you fold a square sheet of paper so that it makes a closed 3D shape, with no overlaps, gaps or extraneous flaps of paper? You cannot, for example, fold the square to make a cube since you will create an overlap or extra flaps.
Solution Yes you can, and here is one: a pyramid with an isosceles triangle as a base.
Hole punch puzzles
For each of the next puzzles, you must take a square piece of paper and fold it, using as many folds as is needed, so that if you punch a single hole through the folded paper you will match the image when the paper is fully unfolded .
3 The X.
4. The diagonal.
5. The ring.
6. A hole punch in the head.
Solution The first fold divides the right 3/4 of the square into half.
Puzzle 1 is taken from The Paper Puzzle Book, puzzle 2 is taken from the Two-Minute Puzzle Book, both excellent and published by World Scientific.
The hole punch puzzles are taken from Mark Chubb’s brilliant blog Thinking Mathematically. You can download printable sheets of these puzzles here. Thanks to World Scientific and Mark Chubb for permissions.
The full reference to the paper mentioned above is: Hawes, ZCK, Gilligan-Lee, KA, & Mix, KS (2022). Effects of spatial training on mathematics performance: A meta-analysis. Developmental Psychology, 58(1), 112-137.
I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.
I’m the author of several books of puzzles, most recently the Language Lover’s Puzzle Book. I also give school talks about maths and puzzles (online and in person). If your school is interested please get in touch.
On Thursday 21 April I’ll be giving a puzzles workshop for Guardian Masterclasses. You can sign up here.