Numbers are like good friends — the more you play with them, the better you understand them! In this chapter we explore numbers from 1 to 99, learn about tens and ones (place value), and practise addition and subtraction.
What will we learn?
We will understand place value (tens and ones), add 2-digit numbers, subtract 2-digit numbers, and use number patterns.
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Key Concepts
Tens and Ones (Place Value):
Every 2-digit number has a tens place and an ones place.
For example: 47 = 4 tens + 7 ones.
Addition: Combining two or more numbers to get a total.
We add the ones first, then the tens.
Subtraction: Finding the difference when one amount is taken away.
We subtract the ones first, then the tens.
Number patterns: Numbers can follow a pattern. For example: 2, 4, 6, 8 (adding 2 each time).
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Worked Examples
What is the place value of 6 in 63?
63 = 6 tens + 3 ones. The digit 6 is in the tens place and its value is 60.
Add 34 + 25.
Ones: 4 + 5 = 9. Tens: 3 + 2 = 5. Answer: 59.
Subtract 46 - 23.
Ones: 6 - 3 = 3. Tens: 4 - 2 = 2. Answer: 23.
What is the missing number in the pattern: 10, 20, ___, 40, 50?
The pattern adds 10 each time. The missing number is 30.
Add 28 + 37.
Ones: 8 + 7 = 15. Write 5, carry 1. Tens: 2 + 3 + 1 (carried) = 6. Answer: 65.
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Common mistakes
- When adding ones that give 10 or more, remember to carry the extra ten to the tens column.
- Do not mix up the tens and ones digits. In 73, the tens digit is 7 and the ones digit is 3.
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Summary
Numbers up to 99 have a tens place and a ones place. We can add and subtract them column by column, starting from the ones. Number patterns help us guess what comes next.