Teacher's Guide Module 1 - Maths Excellence

2. Look at the tens digit.
If it is 5 or more, the hundreds digit becomes one more.
If it is 4 or less, the hundreds digit remains unchanged.
3. Look at the hundreds digit.
If it is 5 or more, the thousands digit becomes one more.
If it is 4 or less, the thousands digit remains the same.
2. 2.1 20 + 10 + 20 = 50
2.2 30 + 10 + 50 = 90
2.3 10 + 20 + 20 = 50
2.4 100 + 200 + 300 = 600
2.5 200 + 100 + 100 = 400
3. “Estimated answer” and “Difference” will be different as a result of the method
applied. Pocket calculator gives correct answer.
4. a) 279
b) 1 660
c) 6 581
d) 2 843
5. Answers will vary – many combinations possible
6. 35 + 15; 47 + 3; 23 + 27
50 + 150; 25 + 175; 10 + 190; 180 + 20; 170 + 30
250 + 750; 400 + 600; 900 + 100; 200 + 800; 990 + 10
6. 250 + 750; 125 + 825; 950 + 50; 450 + 550; 225 + 775; 415 + 585
7. 5 000 + 400 + 80 + + 9 + 300 + 60 + 2 + 1 000 + 500 + 70
= (5 000 + 1 000) + (400 + 300 + 500) + (80 + 60 + 70 +) + (9 + 2)
= 6 000 + 1 200 + 210 + 11
= 7 421
.......................ACTIVITY 2.7
Counting on
Take away 11 400 every time and add the rest
1.3 Keep 1 000s, 100s and 10s apart and add
1.4 Counting on: first 10 000s, then 1 000s, then 100s, then 10s and lastly units