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MENTAL MATH: TiPs & TrIcKs for...

Subtraction I

When working with these operations it's very useful to picture numbers in groups... to fragment them into smaller numbers. Try imagining blocks. For example, 14 - 6 = 8

(fig 6)

Visualize a 14 as a group of 10 and a group of 4.

Then subtract 6 from the first group, that now has 4. This will be add to the second group (4) that remain unchanged, that is  4 + 4 = 8

It's a mater of playing with the numbers, if it were

19 - 11 = 8

(fig 7).

The  19 would be a group of 10 (A) and a group of 9 (B), while the  11 would be a group of 10 (C) and a group of 1 (D).

take off C from A,  A - C = 0,

take D from  B,  B – D = 8;

the total would be  0 + 8 = 8