When I worked as a school inspector I observed at first hand how children who were otherwise highly numerate often lacked arithmetic agility when tackling maths problems. Some commentators attribute this to an over-reliance on calculators. My theory, applicable in the UK at least, was the wholesale adoption of metrication. The metric system and decimal currency have a lot going for them but there's no denying that pre-metrication children had wide exposure to calculation in multiple bases: base 3 for feet and yards; base 12 for inches and feet, and for pennies and shillings; base 20 for shillings and pounds; base 16 for ounces and pounds; base 14 for pounds and stone; base 8 for furlongs and miles, and pints and gallons, etc. I'm always on the lookout therefore for games that encourage arithmetic agility, so I was excited to try Leo Samson's 21X.
21X comprises a deck of 54 cards that look almost like playing cards. Instead tho' of conventional Ace to King cards in four suits, these cards contain a mix of suit symbols but, most important, most cards' value is an algebraic formula: 4X, 10-2X, 12/X, 4N/X, etc. The idea is that players use these to play a variant of Blackjack (aka Pontoon; aka 21; aka Vingt-et-Un). You are dealt two cards. You can set whatever value you like for X just so long as it's an integer (whole number) and it's the same value for all the cards in your hand. You are trying to use the cards to total 21 or as close to it as you can get without going over. You can stick with the two cards you were dealt or you can twist (take another card). If you can make 21, you call out, citing the value you are attributing to X.
So, for example, if I have (X-N) squared and 10-2X, then I can make 21 by declaring X = 7 because, with two cards and X=7, (X-N) squared is 25 and 10-2X is -4.
The bizarre-looking cards are initially daunting but you can simplify the deck and make it more accessible by filleting out cards with some of the more challenging formulae (the 'difficulty level' of each card is shown with a small symbol, making it quick and easy to edit the deck). You can then later step up the algebraic challenge by adding back more cards as players become more familiar with the formulae and the way the game works. Tho' the positioning of the card values could make them potentially awkward for left-handed players, you're not having to fan large hands of cards in 21X (maximum hand size is 5 cards) so this isn't likely to present as an issue.
In just the few days we've been playing 21X our facility with algebraic formulae has sharpened noticeably. This is a puzzle game then that maths teachers might especially welcome for playing with pupils.
Naylor Games are bringing 21X to Kickstarter soon. There are plans to add cards with an additional variable, adding further to the game's educational versatility. We'll add a link to the campaign when it goes live.