Directed Number

2015-16 Y7 Mathematics

Addition & Subtraction

In the section 1.1 to 1.4Students should know numbers with opposite meanings the concepts & usage of positive &

negative numbers order of directed numbers on a number

line how to perform addition & subtraction of

directed numbers with the help of a number line

how to master the rules for removing brackets

how to use addition & subtraction of directed numbers in solving problems

1.1 Positive & Negative Numbers

• Numbers with Opposite meanings

• The concept & usage of Positive & Negative numbers

Numbers with Opposite meanings• Opposite SIGN, i.e. “+” &

“-” • Split into 5 groups, 5 to 6

persons each group• Describe a real-life

situation involving positive, negative numbers & zero

• Distance / Money Transaction / Change in Population

Directed number is a number…• with a “+” or “-” sign at the front.

• Showing both magnitude & direction

• The positions of positive & negative numbers on a number line are symmetrical if zero is taken as the centre.

• Distance between two successive integers are equal

1.2 Directed Numbers & Number Lines

1.2 Directed Numbers & Number Lines

1.2 Directed Numbers & Number Lines

• Order of directed numbers on a number line

A number is greater than any numbers lying on its left.

A number is smaller than any numbers lying on its right.

-4 < 2 -1 > 0

-1 > -3 5 > -3

3 < -3 -4 < -2

Adding a positive number

(+2) + (+3) =

(-3) + (+6) =

0-1 -2 -3 -4 1 3 52 41 3 52 4-4 -3 -2 -1

+(+6)

2 + 3 = 5

-3 + 6 = 3 +

(+3)

When adding a positive number,

the arrow is moving to the RIGHT

A + (+B) = A + B

Subtracting a positive number

(+2) – (+4) =(-3) – (+1) =

0 1 3 52 4-4 -3 -2 -1

- (+4)

-2-4

- (+1)

When subtracting a positive number,

the arrow is moving to the LEFT

A - (+B) = A - B

Adding a negative number

(+4) + (-5) =(-3) + (-1) =

0-4 -3 -2 -1 1 3 52 4

4 – 5 = -1-3 – 1 = -4

When adding a negative number,

the arrow is moving to the LEFT

A + (-B) = A - B

Subtracting a negative number

(+2) - (-3) =(-4) - (-2) =

2 + 3 = 5-4 + 2 = -2

0-4 -3 -2 -1 1 3 52 4

When subtracting a negative number,

the arrow is moving to the RIGHT

A - (-B) = A + B