# Form 1 Unit 7 :Lesson 4 – Multiplication and Division of Directed Numbers

Objective

At the end of this lesson, students should be able to multiply and divide directed numbers.

The rules for multiplying and dividing two directed number are as follows;  Example 1  Solution  Example

Simplify:

a) (–2)(–3)(–4)            b) (–1)(–2)(–1)(–3)(–4)(–2)(–1) Solution     Exponents

Example 1

Simplify: a) (–3)2        b) –32

Solution

1. a) (–3)2= (–3)(–3) = +9                                       ( x = +)
2. b) –32= –(3)(3) = (–1)(9) = –9                         ( x + = )

Note the difference between the above examples.

In the example b) the square “to the power 2” was only on the 3; it was not on the minus sign.  Parentheses or brackets makes all the difference in the two examples.

Example 2

Simplify

1. a) (–5)3                       b) (–2)4

1. a) (–5)3 = (5)(5)(5)
= (25)(5)
125
2. b) (–2)4 = (2)(2)(2)(2)
= + 4 x + 4

= (4)(4)
16

Example 3

a = –2 and b = –6

Work out the following

a) a2                        b)a2 + b2           c) b3 – a2              d) (a – b)2

Solution

a) a2 = –2 × –2 = 4

b) a2 + b2 = (–2 × – 2)+( –6 × –6) = 4 + 36 = 40

c) b2 – a2 = (–6 × –6) – (–2 × –2) = 36 – 4 = 32

d) (a – b)2 = (–2 – –6)2 = (–2 + 6) = (4)2 = 16

B0DMAS

Example 1

Simplify the following.  Solution

In this problem you can see all the different operations. When there is more than one operation involved in a problem, we have to follow the order of operations.

1. 1. Brackets
2. Division or multiplication from left to right
3. Addition or subtraction from left to right

(a) 23 – (5– –7)

(First, carry out the operations inside the brackets, = +)

= 23 – (5 + 7)

= 23 – (12)             (next, remove the brackets )

= 11

(b) 5 × – 4 +  –8   (Remember the order, × before +)

= –20 + –8        (+ = )

= – 20 – 8

= –28

(c) –25 ÷ [ 5 × –2 – (–3 ×5) ]

(In this problem, ( )brackets are inside the [ ] brackets, so first you have     to solve the inner brackets before and the outer brackets.)

= – 25 ÷ [5 × –2 – (–15)]                           (–3 ×5 = –15  )

= – 25 ÷ [–10 – (–15) ]                               (5 × –2 = –10)

= –25 ÷ [–10 + 15]                                      (– – = + )

= –25 ÷ 

= – 5                                                              (– ÷ + = – )

d) –8 + (6 × –3 – 2 ) ÷ –4 – –8                        ( 6 x –3 –2 = –18 –2)

= –8 +(–18 –2 )÷  –4 + 8                                          –18 –2 =–20

= –8 +  –20 ÷ 4                                                          –20 ÷ 4=–5

= –8 – 5

= –13

Unit 7 lesson 4: Exercise 1

Try the following

1) 146 x  –2

2) –100 x  3

3) –72 x  –1

4) 5 x  –18

5) 45 ×–23

6) 20  x   30

7) –35 x  –5

8) 40 x  –7

9) –7 x  –7

10) 14 x  –10

Unit 7 lesson 4: Exercise 2 Evaluate the following Unit 7 Lesson 4: Exercise 3

1) What number do you multiple by –3 to get the following?

a) 6           b) –90                 c) 45               d) 81          e) 21

2) What will you get if you divide -48 by the following?

a) –2 b) –8          c) 12           d) 24              e) +4

3) What number do you divide by –36 to get the following?

a) –9          b) 4            c) 12        d) 6      e) –3

4) Write down six different multiplication problems that will give –12 as the answer.

5) Write down six different division problems that will give –4 as the answer.

6) Put the answers to the calculations in order from lowest to 7) Evaluate the following  8) Evaluate the following 9)Evaluate the following

a) 3 + 9 × –6 2                  b) 13 x 2 – (6 +7)                 c)  (–2–2) × [6 + (–6)]

10) x = –2, y = –3 and z =  – Work out the following:

a) x2 b) y2 + x2            c ) z2 – x2            d) (x – y)2

2019-01-10T10:48:32+00:00
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