Problem (Page 88). In a group of nine coins, eight weigh the same ...

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3.1. ADDITION AND SUBTRACTION 35Definition (Subtraction – Take-Away Approach).Let a and b be any whole numbers and A and B be sets such that a = n(A),b = n(B), and B ✓ A. Thena b = n(A B).“a b” is the di↵erence of a and b, “a” is the minuend, and “b” is the subtrahend.Subtraction – the missing addend approachDefinition (Subtraction - Missing Addend Approach).Let a and b be any whole numbers. Then a b = c if and only if ( () )a = b + c for some whole number c.This approach is useful for learning subtraction facts by relating them to additionfacts via four-fact families:
36 3. WHOLE NUMBERS: OPERATIONS AND PROPERTIESMany subtraction facts can be obtained from an addition facts table.Example (A Two Set, Comparison Model, Using Matching). If Larry has$7 and Judy has $3, how much more money does Larry have?7 3 = 4After matching, we can use either the take-away or the missing addend approach.Note. Subtraction is not closed, for 3 5 does not have a whole number asan answer. What about the other properties we have for addition?Example (Four fact family in base 5).3 5 + 4 5 =12 54 5 + 3 5 =12 512 5 3 5 =4 512 5 4 5 =3 5
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Problem (Page 88). In a group of nine coins, eight weigh the same ...

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