Today’s first puzzle was written by webcomic cartoonist Randall Munroe xkcd and author of the best-selling book what if
For the (certainly) very few readers who have never heard of him, Munroe, a former NASA roboticist, is arguably the world’s leading science humorist.
Today’s challenge, a riff on his classic cartoon about self-reference, is both a puzzle and a meta-joke.
1. Now all together
Find all the possible ways, if any, to fill in the three blanks to make all three statements true.
Today’s second puzzle is an elegant version of the Venn diagram. It was written by RGee Watkins, a maker of wooden block puzzles.
2. One to Venn
The four squares below form a Venn diagram with ten regions, labeled A to J. The letters A to J each stand for a number between 1 and 10, so that no two regions share the same number and all numbers from 1 up to 10 are used. The regions in each square add up to the same number. What value is D, the intersection of all four squares?
I’ll be back at 5pm UK with the solutions. Please NO SPOILERS! Instead, talk about your favorite Munroes, Munros and Monroes.
Both of today’s puzzles are taken from The Mathematical Playground: People and Problems of 31 Years of Mathematics Horizons. Mathematics Horizons is the undergraduate journal of the Mathematical Association of America, and the book, a compilation of its best puzzles, is full of great material. For more information see here.
what if (10th anniversary edition) by Randall Munroe will be released in the UK on November 14th.
My latest book is Think twice: solve the simple puzzles (almost) all get wrong. (In the US it is called Puzzle Me Twiceand out tomorrow.) To support the Guardian and Observer, order your copy from guardianbookshop.com. Delivery charges may apply.
I’ve been doing a puzzle here on alternate Mondays since 2015. I’m always on the lookout for great puzzles. If you want to suggest one, email me.
