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100 × 2 700 = .........................

  • Write a rule for multiplying any number by 100:

Does your rule “work” for 0,2 × 100?

Activity 7:

To recognise and use the characteristics of multiplication with whole numbers [lo 1.12.3]

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?

Activity 8:

To estimate and calculate by means of rounding off [lo 1.8.1]

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 ......................... ......................... .........................

BRAIN-TEASERS!

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 .........................

Activity 9 :

  • To be able to solve problems in context [LO 1.6.1]
  • To be able to use a series of techniques to do calculations [LO 1.10]

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 above-mentioned would you choose if you had to travel? Why?

3. Where is your favourite seat in:

  1. a car
  2. a school bus
  3. a boat
  4. an aeroplane

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
  • Who made the most money with the first trip?
  • If the petrol cost R1,05 for every kilometre that was travelled, how much did Mr Mugathle’s petrol account come to?
  • If all the passengers in Mr Slobo’s taxi were athletes and they had to run back, how far did they run altogether?
  • Explain to the rest of the class how your group calculated the answers.
  • Compare your methods. How do your methods differ?
  • Check the answers, using a pocket calculator.

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Source:  OpenStax, Mathematics grade 5. OpenStax CNX. Sep 23, 2009 Download for free at http://cnx.org/content/col10994/1.3
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