This chapter covers the processes of addition, subtraction, division, and multiplication of signed numbers.

EO1.7 APPLY one of the arithmetic operations of addition, subtraction, multiplication, and division using signed numbers.

Calculator Usage, Special Keys

Change Sign key

Pressing this key changes the sign of the number in the display. To enter a negative number, the number is entered as a positive number and then the change sign key is pressed to convert it to a negative. The display will show a "-" in front of the number.

Addition

Addition of signed numbers may be performed in any order. Begin with one number and count to the right if the other number is positive or count to the left if the other number is negative.

Example:

-2+3=0-2+3

Solution:

Begin with -2 and count 3 whole numbers to the right.

Therefore: -2 + 3 = 1

Example: (-2)+3+4=0-2+3+4

Solution:

Therefore: (-2) + 3 + 4 = 5

Example:

Solution:

Begin with 2 and count 4 whole numbers to the left.

Therefore: (2) + (-4) = -2

Adding numbers with unlike signs may be accomplished by combining all positive numbers, then all negative numbers, and then subtracting.

Example:

Solution:

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 $40. This gives a bill of $40 and adds as negative $40 to his cash balance. Now suppose he returns this window to the store and the manager tears up his bill, subtracting the - $40. This is equivalent of adding +$40 to his cash balance.