Week 8 – Jss 1 Second Term Mathematics Lesson Notes

WEEK 7 MID TERM
PERIODIC TEST.
WEEK 8    ADDITION AND SUBTRACTION (DIRECTED NUMBERS

 8.1    ADDITION AND SUBTRACTION OF DIRECTED NUMBERS.
    In a horizontal number line:

1. When adding, start from the first number, count right along the number line.
   
2. When subtracting, 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 8.1: use number line to find the value of the (a) 3 + 5, (b) -4 – 6, (c) -9 + 12
Solution:

-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
3 + 5 = 8

(b)
-11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3
                    (-4 )–(-6) = -10

1. 

   -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3

    -9 + 12 = 3

 
 
 
 
 DO THESE:

1. Draw a suitable horizontal number line to answer the following
2. 5 – 8
3. 6 – 2
4. (-5) – (-8)
5. 7 + 2
6. 5 + 8

    

2.    Use the rules to answer the following

1. +5 – (+6)
2. 25 + (-55)
3. +24 + (+28)
4. 18 – 68
5. -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.

1. 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 +)

2. 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

1. (+6) + (+9)
2. (+21) – (+9)
3. (+12) + (-5)
4. (+29) + (+13)

Solution:
Note: You need to follow the rules.

1. (+6) + (+9) = 6 + 9 = 15 (same sign gives +)
2. (+21) – (+9) = 21 – 9 = 12 [different sign gives negative sign]
3. (+12) + (-5) = 12 – 5 = 7 [different sign gives negative sign]
4. (+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