Inside Collection (Course): Mathematics Grade 5
I think you already know how important it is to know your tables well. In this learning unit it will help you to multiply quickly and correctly. Let us see how well you know your tables.
1. Take the fruitshaped sweets containing the correct answers out of the jar. Colour them in neatly and then write down the letter of the alphabet written on it. Use these letters to complete the sentence:
_____________ is a shorter way of doing repeated addition.
1.1 5 × 4
1.2 2 × 3
1.3 7 × 7
1.4 7 × 4
1.5 5 × 5
1.6 7 × 3
1.7 6 × 4
1.8 9 × 2
1.9 9 × 7
1.10 9 × 9
1.11 7 × 6
1.12 3 × 5
1.13 8 × 8
1.14 12 × 4
1.15 6 × 12
1.16 9 × 12
1.17 6 × 6
1. Now that you know exactly what factors are, you are probably able to see their important function in multiplication. Factors also help us to test our answers when we multiply. Yes, you are right! We use them when we divide in order to test whether we have multiplied correctly. Now see how many pairs of factors you can write down for the following numbers.
a) 24 = ............ × ............  b) 36 = ............ × ............ 
= ............ × ............  = ............ × ............ 
= ............ × ............  = ............ × ............ 
= ............ × ............  = ............ × ............ 
= ............ × ............ 
2. Let us do some more exercises, using factors. Look at the products (numbers) and then write down suitable factors for them. The first one has been done for you.
42  45  63  54  64 
7 × 6  ......................  ......................  ......................  .................................... 
72  108  48  88  96 
......................  ......................  ......................  ......................  .................................... 
DO YOU STILL REMEMBER?
When you multiply any number by 0, the answer is always 0. (0 × 6 = 0)
Any number multiplied by 1, is that number.(9 × 1 = 9)
Now the factors are supplied to you. All you have to do in your first mental arithmetic test is to complete the multiplication block by writing down the missing answers only. Easy, isn’t it?
X  4  5  6  7  8  9  12 
5  20  ............  30  ............  40  ............  60 
6  ............  30  36  42  ............  54  ............ 
7  28  ............  42  ............  56  ............  84 
8  ............  40  ............  56  ............  72  ............ 
9  ............  ............  54  ............  72  ............  108 
2  48  60  ............  84  ............  108  ............ 
By doubling numbers we can find the answer to a multiplication sum much more easily. Here we can learn from the Egyptians. Work with a friend and see whether you are able to find out how this calculation was done.
28 × 324
1 × 324:  324  (1 × 324) 
Double 324:  648  (2 × 324) 
Double l 648:  1 296  (4 × 324) 
Double 1 296:  2 592  (8 × 324) 
Double 2 592:  5 184  (16 × 324) 
Thus: 28 × 324 =  9 072 
BRAINTEASER!
Calculate the following in the same way as the Egyptians did thousands of years ago:
15 × 241
DID YOU KNOW?
Thus we can also make use of DOUBLING when we want to multiply:
2 × 280 = (200 + 200) + (80 + 80)
= 400 + 160
= 560
1. If you looked carefully at the example above, you would have seen that this method of doubling differs from that of the Egyptians. Can you calculate the following by doubling it in exactly the same way?
1.1 2 × 1 430 =
1.2 2 × 2 315 =
2. We would very much like to use the shortest possible method in Mathematics, because it saves a lot of time, trouble and paper. Calculate the product again by doubling, but this time use a shorter method if you can.
2.1 2 × 14 820 =
2.2 2 × 36 947 =
3. There is another technique that you can use to calculate the product. You can double and halve! This makes it easier to multiply with the “big” numbers. Look carefully at the following:
126 × 5= 63 × 10 (halve 126 ; double 5)= 630
Can you find the following answers by doubling and halving?
3.1 50 × 24  3.2 5 × 346 
BRAINTEASER!
Can you fill in the missing numbers/factors WITHOUT using your calculator?
48  ×  12  =  576  64  ×  10  =  640 
...........  ×  24  =  576  32  ×  ...........  =  640 
12  ×  ...........  =  576  ...........  ×  40  =  640 
6  ×  ...........  =  576  8  ×  ...........  =  640 
...........  ×  ...........  =  576  ...........  ×  ...........  =  640 
Did you discover a pattern?
1. Now let us look at multiplication with multiples of 10 and 100. As we work through the examples, you will see that there are certain rules that you must follow in order to calculate the product. If you apply these rules, you will be able to calculate the answers without doing long computations on paper. Work with a friend and write down the product of the following:
1.1 10 × 6 = ......................... ; 10 × 60 = ......................... ;
10 × 600 = ......................... and 10 × 6 000 = .........................
1.2 10 × 9 = ......................... ; 10 × 90 = ......................... ;
10 × 900 = ......................... and 10 × 9 000 = .........................
1.3 10 × 15 = ......................... ; 10 × 150 = ......................... ;
10 × 1 500 = .........................
1.4 10 × 26 = ......................... ; 10 × 260 = ......................... ;
10 × 2 600 = .........................
Can you now write down a rule for multiplying any number by 10?
Does this “work” for 0,5 × 10?
2. Let us look at multiplication with multiples of 100. Work with the same friend and write down the product of:
2.1 100 × 8 = ......................... ; 100 × 80 = ......................... ;
100 × 800 = .........................
2.2 100 × 13 = ......................... ; 100 × 130 = ......................... ;
100 × 1 300 = .........................
2.3 100 × 27 = ......................... ; 100 × 270 = ......................... ;
100 × 2 700 = .........................
Does your rule “work” for 0,2 × 100?
1. In our previous module we looked at the associative and commutative characteristics of addition – do you remember this? There are similar characteristics of multiplication. Do you want to know how it works? Fill in the missing factors to balance the equasions:
8 x 6 = 6 x ____
23 x ____ = 13 x 23
124 x 85 = ____ x 124
2. Is the following true or false?
2.1 6 × 3 × 4 = 3 × 4 × 6 = 4 × 6 × 3 ..................................................
2.2 (2 × 4) × 5 = (5 × 4) × 2 = 4 × (2 × 5) ..................................................
3. What do you realise from the above examples?
1. To be able to estimate answers is an important skill. If you are good at estimating, it will be easier for you to realise that you may have made a mistake in your calculations. Round off the following numbers first and in this way you will be able to estimate what the product of each of the following will be:
SUM  ESTIMATE  CALCULATOR  DIFFERENCE 
E.g. 19 × 21  400  399  1 
a) 38 × 27  .........................  .........................  ......................... 
b) 99 × 146  .........................  .........................  ......................... 
c) 45 × 69  .........................  .........................  ......................... 
d) 998 × 78  .........................  .........................  ......................... 
e) 409 × 18  .........................  .........................  ......................... 
BRAINTEASERS!
a)Which two numbers, smaller than 10, have 3 factors each?
......................... and .........................
b) Colour in the correct block:
The product of 2 uneven numbers is always an  EVEN  UNEVEN  number. 
c) Which two numbers have a product of 48 and a sum of 16?
......................... and .........................
Let’s do some brainstorming now. Your teacher will give you the necessary paper.
1. Split up into groups of three and, as quickly as possible, make a list of all the means of transportation that exist in our country.
2. Which of the abovementioned would you choose if you had to travel? Why?
3. Where is your favourite seat in:
4. Now see whether you are able to solve the following problems:
Messrs Slobo, Mugathle and Sisula have each bought a brand new taxi with which to transport passengers. For their first trip their plans are the following:
Owner  Amount per person  Number of passengers  km travelled 
Slobo  R15,80  13  76 
Mugathle  R14,60  14  84 
Sisula  R16,25  12  59 
1. In Activity 1.9 you used your own techniques and strategies to solve the problems. In your feedback to the class you probably noticed that there are many ways in which numbers can be multiplied. Split up into groups of three. Read the following problem and then see whether you can understand all the different solutions.
Chairs must be arranged in rows in a hall. There must be 23 rows with 16 chairs in each row. How many chairs are needed?
1.1 I calculate 23 × 16 like this:
23 = 10 + 10 + 10 + 1 + 1 + 1
23  × 16 
10  160 
10  160 
2  32 
1  16 
23  368 
1.2 I calculate 23 × 16 in this way:
23 = 20 + 3
16 = 10 + 6
Thus: (20 + 3) × (10 + 6)
20 × 10 = 200
20 × 6 = 120
3 × 10 = 30
3 × 6 = 18
368
1.3 I divide 16 into its factors:
23 × 16 = 23 × 2 × 8
= 23 × 2 × 2 × 4
= 46 × 2 × 4
= 92 × 4
= 368
1.4 I calculate it like this:
23 × 16 = (23 × 20) – (23 × 4) (I took 4 × 23 too much, so I had to subtract it)
= (23 × 10 × 2) – (23 × 4)
= 460 – 92
= 368
1.5 My method is shorter!
23
× 16
18 (6 × 3)
120 (6 × 20)
30 (10 × 3)
200 (10 × 20)
368
1.6 My method is shorter still!
^{1}2 3
× 1 6
1 3 8
2 3 0
3 6 8
1.7 Which method do YOU choose?
Why?
1. It is better to use a technique that you understand perfectly when you have to do a calculation. Use any method and calculate the following:
1.1 58 × 29  1.2 76 × 54 
2. In the following activity we are going to see how certain factors form patterns when we multiply them by each other. We are also going to use the pocket calculator to help us with our calculations.
2.1 Using the pocket calculator, complete the following:
77 × 13 = ....................
77 × 26 = ....................
77 × 39 = ....................
77 × ............. = 4 004
77 × ............. = 5 005
77 × 78 = ....................
77 × 91 = ....................
2.2 Predict the answer without using your calculator: 77 × ............. = 8 008
77 × 117 = .............
2.3 What is the pattern in the above example?
2.4 Calculate the following, first without using the pocket calculator, and then by using it.
1 × 9 + 2 = .........................
12 × 9 + 3 = .........................
123 × 9 + 4 = .........................
................. × 9 + 5 = 11 111
12 345 × 9 + ........ = 111 111
................. × 9 + ........ = .........................
................. × 9 + ........ = .........................
2.5 Predict now without your calculator:
12 345 678 × 9 + 9 = .
123 456 789 × 9 + 10 =
2.6 Can you explain to a friend the pattern in the above example?
Let us see whether you can improve on your previous mental arithmetic test. This exercise will serve as preparation for the activities to follow. Fill in the missing answers of the MARKED BOXES ONLY.
X  2  6  7  8  9  10  12  100 
5  .........  ........  .......  
6  ......  .......  
7  ........  .......  .......  
8  ......  ........  
9  ......  ........  
36  .......  ........  ......  
48  .......  ........  .......  
124  .......  ........  ....... 
By now you know how to multiply by smaller numbers. Now we are going to see whether you are also able to do calculations with bigger numbers. Split up into groups of 3 and ask your teacher to give you the paper you need. Then read the instructions very carefully.
Michaela and her friends visited the zoo and heard the following interesting facts: a hippopotamus eats 45 kg of fodder per day, while a large bull elephant needs 225 kg of fodder per day!
1. How many kilograms of fodder will 329 hippopotamuses eat per day?
2. How many kilograms of fodder must the zoo buy per day to feed 76 bull elephants?
3. If the entrance fee was R15 per person and 475 people visited the zoo that day, how much money was taken at the entrance gate?
4. Explain to the rest of the class how your group calculated the answers.
5. Compare your methods. How do the various methods differ from each other?
6. Use a pocket calculator to check the answers.
1. In the previous activity you probably noticed that there is more than one method to do multiplication. Split up into groups of 3 again. Look carefully at the solutions to the following problem and explain the methods to one another.
Mrs Cele sells clothes. There are 46 different pairs of jeans and 238 different shirts. How many combinations can she make up?
1.1 I calculate 46 × 238 in this way
238 × 46 = (200 + 30 + 8) × (40 + 6)
200 × 40 = 8 000
30 × 40 = 1 200
8 × 40 = 320
200 × 6 = 1 200
30 × 6 = 180
8 × 6 = 48
10 948
1.2 I write it in this way:
238
× 46
48 (8 × 6)
180 (30 × 6)
1 200 (200 × 6)
320 (40 × 8)
1 200 (40 × 30)
8 000 (40 × 200)
10 948
1.3 My method looks like this:
^{2}2 ^{4}3 8
× 4 6
1 4 2 8
9 5 2 0
1 0 9 4 8
2. Now use any method that you understand and with which you feel comfortable, and calculate the product of:
2.1 576 × 47
2.1 576 × 47
CHALLENGE!
Can you calculate the product of the following by using the method shown in 1.3?
1. 347 × 251
2. 526 × 438
ANOTHER BRAINTEASER
Study the following sum carefully: 24 × 13 = 377
One of the digits is incorrect. Can you find out which one it is? ..............
What must it be? .........................
Let’s go out to dinner.
This assignment is for your portfolio. Your teacher will go through it with you and explain exactly what you are expected to do. Make sure that you understand perfectly before you start. Remember to work neatly.
Read the following menu carefully:
Form groups of three. Your group decides to eat something from each section of the menu. To make it easier for the waiter, each person in your group chooses the same soup, starter, main course and dessert.
Decide what you are going to order and then calculate your account. Use the block below. You may use a calculator. First estimate what the meal will cost the group. ..............................
Please work in the given blocks in order to answer the following questions:
If each of you has R85, will your group have enough money to pay the bill? .........…
If this is so, how much change will your group receive?
How much will you tip the waiter? ......................... Why?
Let us do a bit of research.
At which restaurant do you like eating the most?
Why?
According to you, what is a ‘MUST’ for a restaurant to be successful?
Can you think of any ‘MUST NOT’S’?
Visit any two restaurants of your choice and compare their menus and prices. Write down what you will report back to the class.
Learning outcomes(LOs) 
LO 1 
Numbers, Operations and RelationshipsThe learner will be able to recognise, describe and represent numbers and their relationships, and to count, estimate, calculate and check with competence and confidence in solving problems. 
Assessment standards(ASs) 
We know this when the learner: 
1.2 describes and illustrates various ways of writing numbers in different cultures (including local) throughout history; 
1.3 recognises and represents numbers in order to describe and compare them: 
1.3.6 multiples of singledigit numbers to at least 100; 
1.3.7 factors of at least any 2digit whole number; 
1.6 solves problems in context including contexts that may be used to build awareness of other Learning Areas, as well as human rights, social, economic and environmental issues; 
1.6.1 financial (including buying and selling, profit and loss, and simple budgets); 
1.8 estimates and calculates by selecting and using operations appropriate to solving problems: 
1.8.1 rounding off to the nearest 5, 10, 100 or 1 000; 
1.8.4 multiplication of at least whole 3digit by 2digit numbers; 
1.8.5 division of at least whole 3digit by 2digit numbers; 
1.9 performs mental calculations: 
1.9.2 multiplication of whole numbers to at least 10 × 10; 
1.10 uses a range of techniques to perform written and mental calculations with whole numbers: 
1.10.1 adding and subtracting in columns; 
1.10.4 doubling and halving; 
1.10.5 using a calculator; 
1.11 uses a range of strategies to check solutions and judge the reasonableness of solutions; 
1.12 recognises, describes and uses:1.12.1 the reciprocal relationship between multiplication and division (e.g. if 5 × 3 = 15 then 15 3 = 5 and 15 5 = 3);1.12.3 The commutative, associative and distributive properties with whole numbers (the expectation is that learners should be able to use the properties and not necessarily know the names). 
LU 2 
Patterns, functions and algebraThe learner will be able to recognise, describe and represent patterns and relationships, as well as to solve problems using algebraic language and skills. 
We know this when the learner: 
2.2 describes observed relationships or rules in own words; 
2.6 determines, through discussion and comparison, the equivalence of different descriptions of the same relationship or rule presented:

ACTIVITY 2
1. (a) 24 x 1 (b) 36 x 1
6 x 4 9 x 4
3 x 8 6 x 6
2.
7 x 6  9 x 5  7 x 9  9 x 6  8 x 8; 32 x 2 
9 x 8  12 x 9  6 x 8  8 x 11  12 x 8; 32 x 3 
ACTIVITY 3
20  25  30  35  40  45  60  
24  30  36  42  48  54  72  
28  35  42  49  56  63  84  
32  40  48  56  64  72  96  
36  45  54  63  72  81  108  
48  60  72  84  96  108  144 
BRAIN TEASERS
9. 1 x 241 : 241 (1 x 241)
Double 241 : 482 (2 x 241)
Double 482 : 964 (4 x 241
Double 964 : 1 928 (8 x 241)
615
ACTIVITY 5
1.1 (1 000 + 1 000) + (400 + 400) + (30 + 30)
2 000 + 800 + 60
= 2 860
1.2 (2 000 + 2 000) + (300 + 300) + (10 + 10) + (5 + 5)
4 000 + 600 + 20 + 10
= 4 630
2.1 (14 000 + 14 000) + (800 + 800) + (20 + 20)
28 000 + 1 600 + 40
= 29 640
2.2 (36 000 + 36 000) + (900 + 900) + (47 + 47)
72 000 + 1 800 + 94
= 73 894
3.1 = 100 x 12 3.2 = 10 x 173
= 1 200 = 1 730
BRAIN TEASERS
24 20
96 80
3 x 192 4 x 160
Halve multiplicand
Double multiplier
ACTIVITY 6
1.1 60; 600; 6 000; 60 000
1.2 90; 900; 9 000; 90 000
1.3 150; 1 500; 15 000
1.4 260; 2 600; 26 000
Add a naught only to multiplier.
2.1 800; 8 000; 80 000
2.2 1 300; 13 000; 130 000
2.3 2 700; 27 000; 270 000
Add two noughts to multiplier.
ACTIVITY 7
1. 8 x 6 6 x 8 23 x 13 13 x 23 124 x 85 85 x 124
2. (a) true
3. It does not matter in which order you multiply.
ACTIVITY 8
1. (a) 1 026
BRAIN TEASERS
(a) 4 9
own answer
own answer
ACTIVITY 11
1.1 1 628
1.2 4 104
2.1 1 001
2 002
3 003
52
65
6 006
7 007
2.2 104
9 009
2.3 Multiplier becomes 13 times more each time.
2.4 11
111
1 111
1 234
6
123 456 7 1 111 111
1 234 567 8 11 111 111
2.5 111 111 111
1 111 111 111
ACTIVITY 12
x  2  6  7  8  9  10  12  100 
5  30  45  
6  48  72  
7  42  63  84  
8  56  96  
9  72  108  
36  72  360  3 600  
48  96  480  4 800  
124  248  1 240  12 400 
ACTIVITY 14
2.1 27 072
2.2 26 358
1. 347
x 251
___
347
17 350
69 400
______
87 097
2. 526
x 438
_____
4 208
15 780
210 400
_______
230 388
4
9