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1.1 (a) 510 (b) 810 (c) 860 (d) 1 400 (e) 1 860
1.2 (a) 800 (b) 300 (c) 2 500 (d) 1 700
2.2
a) 16 00 － 10 000 = 6 000
b) 98 000 - 46 000 = 52 000
c) 642 000 - 23 6000 = 406 000
d) 926 000 - 759 000 = 167 000
e) 2468000 - 1129000 = 1339000
1. As with addition we can subtract more easily by rounding off numbers. In this way we estimate what the answer should be approximately! Work with a friend. Take turns to say the answers out loud to each other. Check the answers with a calculator. Feel free to ask your educator's help where needed.
1.1 Subtract by rounding off both numbers to the nearest 10:
a) 567 – 63
b) 901 – 87
c) 885 – 25
d) 1 454 – 49
e) 1 999 – 138
1.2 Round both numbers to the nearest 100 and subtract:
a) 973 – 214
b) 1 259 – 993
c) 6 048 – 3 512
d) 9 999 – 8 234
2. Let us look at different ways in which the difference between big numbers can be calculated!
2.1 Can you still remember?
Explain to friend how to round off to the nearest 1 000.
2.2 Complete the table by rounding off to the nearest 1 000:
NUMBER 1 | NUMBER 2 | DIFFERENCE | |
e.g . 4 386 – 1 274 | 4 000 | 1 000 | 3 000 |
a) 15 980 – 9 621 | .......................... | .......................... | .......................... |
b) 98 102 – 46 147 | .......................... | .......................... | .......................... |
c) 642 368 – 236 419 | .......................... | .......................... | .......................... |
d) 926 135 – 758 910 | .......................... | .......................... | .......................... |
e) 2 468 265 – 1 128 651 | .......................... | .......................... | .......................... |
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 1.8: We know this when the learner 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;
1.8.2 addition and subtraction of whole numbers with at least five digits.
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