Learning Objectives
- Understand place value of tens and ones clearly
- Add two-digit numbers without carrying
- Subtract two-digit numbers without borrowing
- Solve addition and subtraction word problems
- Write numbers in expanded form
Key Concepts
Place Value
In a two-digit number, the digit on the right is in the ones place and the digit on the left is in the tens place. In the number 47, the 4 is in the tens place and means 40. The 7 is in the ones place and means 7. So 47 = 40 + 7. Understanding place value is very important for adding and subtracting.
Adding Two-Digit Numbers
To add two-digit numbers, first add the ones, then add the tens. For example, 23 + 14: Add ones: 3 + 4 = 7. Add tens: 2 + 1 = 3. The answer is 37. Always start adding from the ones place (the right side).
Subtracting Two-Digit Numbers
To subtract two-digit numbers, first subtract the ones, then subtract the tens. For example, 48 โ 25: Subtract ones: 8 โ 5 = 3. Subtract tens: 4 โ 2 = 2. The answer is 23. Always start subtracting from the ones place.
Word Problems with Addition
A shop has 32 red balloons and 25 blue balloons. How many balloons are there in total? We add: 32 + 25. Ones: 2 + 5 = 7. Tens: 3 + 2 = 5. Total = 57 balloons. Words like "total", "altogether", and "in all" mean we should add.
Word Problems with Subtraction
Raju has 46 marbles. He gives 13 marbles to his friend. How many marbles does he have left? We subtract: 46 โ 13. Ones: 6 โ 3 = 3. Tens: 4 โ 1 = 3. Answer = 33 marbles. Words like "left", "remaining", and "how many more" mean we should subtract.
Important Terms
- Place value: The value of a digit depending on its position in the number
- Tens place: The position on the left in a two-digit number
- Ones place: The position on the right in a two-digit number
- Expanded form: Breaking a number into tens and ones, like 56 = 50 + 6
- Sum: The answer when we add two numbers
- Difference: The answer when we subtract two numbers
Quick Revision
- In 63: 6 is in tens place (60) and 3 is in ones place (3)
- To add: first add ones, then add tens
- To subtract: first subtract ones, then subtract tens
- Always start from the ones place (right side)
- "Total" and "altogether" mean addition; "left" and "remaining" mean subtraction
- Practice: 35 + 22 = 57, 69 โ 34 = 35, 41 + 28 = 69