SIGNED NUMBERS
Review of Introductory Mathematics
Adding numbers with unlike signs may be accomplished by combining all positive numbers, then
all negative numbers, and then subtracting.
Example:
10 + (–5) + 8 + (–7) + 5 + (–18) =
Solution:
+10 – 5 + 8 – 7 + 5 – 18 =
+10 + 8 + 5 – 18 – 7 – 5 =
+23 – 30 = –7
Subtraction
Subtraction of signed numbers may be regarded as the addition of numbers of the opposite signs.
To subtract signed numbers, reverse the sign of the subtrahend (the second number) and add.
For example, one could treat his incomes for a given month as positive numbers and his bills as
negative numbers. The difference of the two is his increase in cash balance. Suppose he buys
a window for . This gives a bill of and adds as negative to his cash balance. Now
suppose he returns this window to the store and the manager tears up his bill, subtracting the -
. This is equivalent of adding + to his cash balance.
Example:
a – b =
a + (–b)
Solution:
(+3) – (+5)
=
(+3) + (–5)
= –2
(–4) – (–1)
=
(–4) + (+1)
= –3
(–5) – (+8)
=
(–5) + (–8)
= –13
(+7) – (–2)
=
(+7) + (+2)
= +9
MA-01
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