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Mathematics

Number concept, addition and subtraction

Subtraction

Educator section

Memorandum

1.1 27 848

1.2 18 121

1.3 254 706

2.1 8 486 – 5 456 = 3 030

84 381 – 54 351 = 30 030

86 488 – 56 455 = 30 033

816 823 – 516 523 = 300 300

814 886 – 514 556 = 300 330

2.2 297 300

3.1 (b) R27 414

3.2 (a) 22 526

(b) 65 778

(c) 668 544

Puzzle

(a) 378 – 111 = 267 – 110 = 157 – 10 = 147

(b) 2 598 – 1 111 = 1 487 – 1 111 = 376 – 110 = 266

(c) 14 210 – 110 = 14 100 – 100 = 14 000

Leaner Section

Content

Activity: to be able to solve problems in context [lo 1.10]

To use strategies to check solutions [lo 1.11]

1.1 __________ = 54 321 – 26 473

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1.2 __________= 63 904 – 45 783

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1.3 __________= 486 213 – 231 507

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2. 2.1 Let's have a race! See if you can beat your partner, but remember to work neatly!

  • Take a good look at each number.
  • Replace the figure 8 with a 5 in each instance.
  • Write the new number right below the earlier one.
  • Then calculate the difference between the 2 numbers and write the answer in the last space.

e.g.

2.2 What is the difference between the biggest and the smallest answer?

_____________________________________________________________________

2.3 Compare your answers with those of your partner.

2.4 Check your answers with the help of a pocket calculator.

3. What follows is still another technique to calculate the difference between two numbers.

3.1 Work in groups of three again. Read the following problems attentively and explain the solutions to one another.

a) Kayla's father buys a brand new Renault Scenic for R147 293 and Wayne's father buys a second-hand car for R69 475. How much more does Kayla’s father pay than Wayne's father?

Kayla's father pays R77 818 more.

b) Roberto frequently has to make overseas phone calls and his telephone account comes to R30 000. Carli uses her cell phone to make telephone calls and her account comes to R2 586. By what amount is Carli's account less than Roberto's account?

Carli pays R27 414 less.

3.2 Calculate the following by making use of the above method:

a) __________= 42 063 – 19 537

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b) __________= 264 136 – 198 358

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c) __________= 900 000 – 231 456

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TIME FOR SELF-ASSESSMENT

We have now studied different techniques / strategies to do and to check calculations. How do YOU feel about the work we have just completed?

Assess yourself by circling the figure in the applicable column.

** COMPLETELY UNCERTAIN SLIGHTLY CERTAIN FAIRLY CERTAIN VERY CERTAIN
I can round off correctly to the nearest 1 000 1 2 3 4
I can subtract by adding 1 2 3 4
I can estimate the difference by means of rounding off 1 2 3 4
I can subtract by rearranging numbers in extended notation 1 2 3 4
I can work with negative numbers 1 2 3 4
I can subtract vertically 1 2 3 4

Puzzle!

You may only use the following keys of your calculator:

1 ; – ; 0 ; =

  • See if you are able to change the first number into the second

number!

e.g. Change 1 416 to 285

1 416 – 1 110 = 306 – 11 = 295 – 10 = 285

a) Change 378 into 147

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b) Change 2 598 into 266

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c) Change 14 210 into 14 000

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Assessment

Learning Outcome 1: The 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 Standard 1.10: We know this when the learner uses a range of techniques to perform written and mental calculations with whole numbers;

1.10.1 adding and subtracting in columns.

Assessment Standard 1.11: We know this when the learner uses a range of strategies to check solutions and judge the reasonableness of solutions.

Questions & Answers

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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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