Mathematics
Subtraction
Educator section
Memorandum
Leaner section
Content
Activity: to calculate by selecting operations appropriate to solving problems [lo 1.8.1]
1. It is still important to remember how to round off numbers, because this is a method that you may be able to use to quickly calculate the difference.
1.1 Work with a partner to determine the difference, by rounding off both numbers to the nearest 10. Take turns to give the answers.
a) 276 – 95
b) 415 – 109
c) 647 – 142
d) 999 – 351
2. Can you calculate the difference between the following numbers quicker than your partner? First round off the numbers to the nearest 100.
2.1 1 325 – 876
2.2 3 764 – 1 321
2.3 6 009 – 4 245
2.4 9 999 – 7 908
How well do you remember?
Complete the following:
A prime number is a number that_________________________________________
____________________________________________________________________
____________________________________________________________________
An even number is._____________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Brainteaser!
Two prime numbers can be subtracted to give an even number as answer, e.g. 19 – 5 = 14
Can you find the correct prime numbers to make the following number sentences true?
1. __________________ – __________________ = 6
2. __________________ – __________________ = 28
3. __________________– __________________ = 48
4. __________________ – __________________ = 60
5. 88 = __________________ – __________________
6. 90 = __________________ – __________________
7. 52 = __________________ – __________________
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 1.8: We know this when the learner estimates and calculates by selecting and using operations appropriate to solving problems that involve:
1.8.1: rounding off to the nearest 5, 10, 100 or 1 000.