Directed numbers Mathematics JSS 1 Second Term Lesson Note for Week Eight

Second Term Lesson Note for Week Eight

Class : JSS 1

Subject : Mathematics

Topic : Directed Numbers

Duration : 80 Minutes

Period : Double Period

Reference Book :

• Essential Mathematics for Junior Secondary School, JSS 1.
• Lagos State Unified schemes of work for Junior Secondary School, JSS 1 – 3.
• Online Resources

 

Instructional Material : Chart showing the directed numbers on a number line.

Learning Objectives : By the end of the lesson learners will be able to :

i. Explain the meaning of directed numbers

ii. Describe a number line

iii. Solve word problems on directed numbers using number line.

 

Content :  

ADDITION AND SUBTRACTION OF DIRECTED NUMBERS.

A number line is the representation of numbers on a line.

A number line could be made up of

(a) Positive values only

(b) Positive and negative values with zero as mid point.

On a number line, we read the numbers either horizontally to the right or to the left.

When adding, we start from the first number, count right along the number line.

When subtracting, we start from the first number, count left along the number line.

NOTE: that in a horizontal number line, number to the right of zero are positive and to the left are negative.

Example : Use number line to find the value of the following :

(a) 3 + 5,          (b) -4 – 6,         (c) -9 + 12

Solution:

(a) 

3 + 5 = 8

You start from 3, count 5 steps to the right. This gives 8.

 

(b). (- 4 ) – (+ 6) = -10

You start from – 4, count 6 steps to the left. This gives – 10.

(c) – 9 + 12 = + 3

You start from – 9, count 12 steps to the right hand side. This gives + 3.

 

DO THESE:
Draw a suitable horizontal number line to answer the following :
1. 5 – 8

2. 6 – 2

3. (-5) – (-8)

4. 7 + 2

5. 5 + 8

2. Use the rules to answer the following
i.) +5 – (+6)

ii.) 25 + (-55)

iii.) +24 + (+28)

iv.)  18 – 68

v.)  -7 + 5 – 2 + 7 -10 -3

8.2 RULES FOR ADDITION AND SUBTRACTION

Note : You can carry out the addition and subtraction without drawing the number line using the rules below.
Replace the same signs that appear together by a positive sign. [+ + = +],  [ – – = -].

Examples +7 + (+5) = 7+5 = 12 (same sign gives +)

+6 – (-8) = 6 + 8 = 14 (same sign gives +)

Replace two different signs that appear together by a negative sign. [+ – = -],[- + = -].

Examples +8 + (-5) = 8 – 5 = 3 [different sign gives negative]

+9 – (+4) = 9 – 4 = 5 [different sign gives negative sign].

Note : To subtract two numbers with different signs, subtract the smaller number from the larger number and then place the sign before the larger number in front of your answer.

Example 8.2: Find the value of the following
i. (+6) + (+9)
ii. (+21) – (+9)
iii. (+12) + (-5)
iv. (+29) + (+13)

Solution :
Note: You need to follow the rules.
(+6) + (+9) = 6 + 9 = 15 (same sign gives +)
(+21) – (+9) = 21 – 9 = 12 [different sign gives negative sign]
(+12) + (-5) = 12 – 5 = 7 [different sign gives negative sign]
(+29) + (+13) = 29 + 13 = 42 (same sign gives +)

ASSIGNMNET:
EXERCISE 10.2 NO 3(A,C,E, M,O) PAGE 114
EXERCISE 10.3 NO 2( E,F,G,H), NO 5 ( A,B,C,D), PAGE 116 and 117