# Thief maths

Ideas and inspiration across the curriculum

Here is a game that I have used to help children who are having difficulty with sums in key stage 2. I'll use the subtraction 328 - 193 to explain how to play. First make a set of cards, nine with "100" written on them, 19 with "10" and 19 with "1". Have several blank cards and a pen to hand. When you are ready to play, write the sum on the board and write the number to be subtracted on one of the blank cards.

Ask for five volunteers, the first to hold the "100" cards, the second the "10"s and the third the "1"s; the fourth is to be the thief and the fifth the exchanger.

Write 328 - 193 = on the board, and "193" on one of the blank cards. The first child holds three "100"s, the second two "10"s and the third eight "1"s. The thief holds the "193" card.

The exchanger sits on the floor with the left-over cards in three neat piles ("100"s, "10"s and "1"s). The thief steals three "1" cards from the third child (holding the "1"s) then moves on to the second child (who is holding the "10"s). Heshe tries to steal nine "10" cards but cannot. So the second child grabs one "100" card from the first child.

The exchanger then pops up and says: "I'll swap that" and, taking the "100" card which the second child has just grabbed, swaps it for 10 "10" cards and gives them to the second child. The thief can then steal nine "10" cards from the second child and lastly one "100" card from the first child.

The thief then runs back to hisher seat to check heshe has one "100", nine "10" and three "1" cards, while the first, second and third children hold up their cards for all to see.

The exchanger then writes the answer (which these three children are now holding up) on the board.

Less able children can play without an exchanger, using carefully selected sums which need no exchanging (eg, 458 - 123). More able children can perform two exchanges (eg, 234 - 178) or you can make them cards which include 1,000s, 10,000s and so on.

Anne Sweeney

Year 4 teacher, Herries School, Windsor and Maidenhead

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