![]() 32 can be partitioned into 20 + 12, so this subtraction can be recalculated as (20 – 10) + (12 – 8) Partitioning is important here in understanding why exchanging works. Understanding exchanging in column subtraction: 32 – 18 may be first calculated as (30 – 10) + (2 – 8) until children realize that they can’t subtract 8 from 2 without reaching a negative number. ![]()
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