Maths game – “Twenty is Plenty”

I came up with this game idea last month to use in a primary school maths workshop on numeracy skills. It’s based on Blackjack/Pontoon but I wanted a simpler version that didn’t look like gambling.

twentyThe aim of the game is to get a score as close to 20 as possible but without going over. (Hence the speed limit sign. And yes I know the speed limit isn’t a target to aim for!)

Rather than use playing cards I used dice. Each team received a die and all the groups rolled at the same time. The number was that team’s score. The rolling was repeated and the new number added to the score. I got the pupils to tell me their total score each time.

At some point there’s a danger that the roll will make the score above 20 so the team has to decided at what point to stop rolling. You can use this opportunity to talk about probabilities. I found that the majority of teams became very competitive and took big risks by keeping on rolling even when their score was 18 or 19.

In terms of practicalities I split a class into 4 groups. Each group sat in a line one behind the other. The first person rolled the dice, added the score up, passed the dice to the next person and then went to sit at the back of the line. That way everyone got a chance. Towards the end of the game the group got to vote on their decision to stop or continue rolling. I let them re-enter the game at a later stage.

Extensions

There are lots of ways you can vary or extend this depending upon time and ability. You could have a larger target number. Use two or more dice each time. Use playing cards instead of dice. Why not include negative numbers on the cards? You’d need to make sure there was more positive than negative numbers though!

Keep a cumulative score of wins if the game is played multiple times. It could be used as a quick time filler in the classroom and the wins counted up over the period of a week/month/term.

For more advanced groups they could calculate the probabilities and the average number of throws you’d need to reach 20.

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