Page 28 - BUSINESS MATHEMATICS MODULE 1 (WHOLE)_revised 10.20.2020

LESSON 2: B. SUBTRATION

• Consider the expression 7 - 4. Since the subtrahend is positive four. Following the rule
of subtraction, positive four will become negative four and we will proceed to do the

addition operation that is 7 + -4. Applying the rules of adding sign numbers, the signs
are different then we will subtract the smaller absolute value from the larger

absolute value, thus we have the equation 7 + -4 = 3 since seven have the larger absolute
value and seven bears a positive sign, therefore, the result is positive three (3).

Subtraction Addition

− 4 → (+) − (+)4 → (+) + (-)4 =(+) or simply 7 + -4 = 3.

• Consider the expression 4 - 7. Positive seven is the subtrahend, then we will have 4 + -
7 and again applying the rules of adding sign numbers, the signs are different then we

will subtract the smaller absolute value from the larger absolute value, thus we have

the equation 4 + -7 = -3. since seven is a larger absolute value and seven bears a
negative sign therefore the result is negative three (3).

Subtraction Addition

4 − 7 → (+)4 − (+) → (+)4 + (-) =(-) or simply 4 + -7 = 3.

Note: Since we change the sign of the subtrahend and we proceed to addition, we can apply

the commutative property. 7 + -4 = -4 + 7 and 4 + -7 = -7 + 4.

Generally speaking, before you perform the subtraction operation- it is safer to change
the subtrahend and proceed to the addition operation.

Subtracting Numbers with More Than One Digit

We may encounter problems in subtracting numbers. This takes place, for example, if

a number in the units-place of the subtrahend has a larger value than the number in the minuend
in the same place.

73 Minuend
− 48 Subtrahend
? Difference
We cannot subtract 8 from 3 and get an answer that is a whole number, To solve this

problem, we can regroup the units and tens in the minuend (Recall the associative principle of
addition).

73 minuend = 70 + 3 = 60 + 13 =
− 48 subtrahend = 40 + 8 = 40 + 08 =
20 + 05 = 25 (difference)
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