Here’s a game to play with a grown-up! It is a version of a well known game called Nim.
How do you play?
You'll need a grown-up to play with.
Start with the Got It target 23. The grown-up chooses a whole number from 1 to 4. Then take turns to add a whole number from 1 to 4 to the running total. The person who hits the target of 23 wins the game. Play the game several times, swapping who goes first. To change the game, choose a new Got It target or a new range of numbers to add on.
Can you find a winning strategy?
Can you always win?
Does your strategy depend on whether or not you go first?
When is it better to go first and when is it better to let the grown-up go first?
Can you work out a winning strategy for any target?
Can you work out a winning strategy for any range of numbers?
Notes for grown-ups
Stop the clock helps children to practise simple addition and subtraction. However, the real challenge is to find a winning strategy that always works and this involves working systematically, conjecturing, refining ideas, generalising and using knowledge of factors and multiples.
have a lower target and a shorter range of numbers (e.g. 10, using 1 and 2). Note down running totals.
play without writing anything down, or play a variation where a player cannot add the same number as that used previously by the opponent.
Repeat the game, aiming to find a winning strategy, then talk together about how it was found.
There's a classroom version of this game here.