Subtraction snake game
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The subtraction snake game is a material defined as psycho-arithmetic, and should only be presented to children after the positive addition snake has been presented. The purpose of this material is to enable children to carry out small unit subtractions almost mechanically, thus introducing them to mental calculation. It consists of a box with a series of coloured sticks representing real quantities and sticks representing quantities that do not exist; a box with coloured positive sticks from 1 to 9 (real numbers); a box with grey negative sticks from 1 to 9 (unreal numbers); after the fifth bead there is a division sign; a box with black and white positive change sticks from 1 to 9 and a box with 10 golden tens.