Class 2 — Mathematics
Addition and Subtraction with Regrouping and Word Problems
Class 2
- ✓By the end of this lesson students will be able to add two 2-digit numbers with regrouping.
- ✓By the end of this lesson students will be able to subtract a 2-digit number from another 2-digit number with regrouping.
- ✓By the end of this lesson students will be able to identify the correct operation (addition or subtraction) in simple word problems.
- ✓By the end of this lesson students will be able to solve word problems involving addition and subtraction with regrouping.
Key concepts
When we add numbers, sometimes the sum of the digits in the Ones place is 10 or more. In such cases, we 'regroup' or 'carry over' the Tens to the Tens place. For example, if 7 Ones + 5 Ones = 12 Ones, we write 2 in the Ones place and carry over 1 Ten to the Tens place.
When we subtract numbers, sometimes the digit in the Ones place of the top number is smaller than the digit in the Ones place of the bottom number. In such cases, we 'regroup' or 'borrow' 1 Ten from the Tens place and add it to the Ones place. This makes the Ones digit larger so we can subtract. For example, if we need to subtract 7 Ones from 2 Ones, we borrow 1 Ten (which is 10 Ones) from the Tens place. So, 2 Ones becomes 12 Ones, and the Tens digit decreases by 1.
Word problems are maths problems told in sentences. To solve them, we need to read carefully and understand what is being asked. Look for keywords:\nFor Addition: 'total', 'altogether', 'in all', 'sum', 'more than'.\nFor Subtraction: 'left', 'remaining', 'difference', 'how many more', 'take away'.
Key facts to remember
- 1When the sum of Ones digits is 10 or more, we regroup 10 Ones as 1 Ten and carry it over to the Tens place.
- 2When the Ones digit of the top number is smaller than the Ones digit of the bottom number in subtraction, we regroup 1 Ten from the Tens place to the Ones place (1 Ten = 10 Ones).
- 3Always start addition and subtraction from the Ones place, then move to the Tens place.
- 4Keywords like 'total', 'altogether', 'in all' usually mean addition.
- 5Keywords like 'left', 'remaining', 'difference' usually mean subtraction.
- 6Always write numbers in columns, aligning Ones under Ones and Tens under Tens.
Worked examples
Example 1
Add 37 and 25.
Answer
62
Example 2
Subtract 18 from 53.
Answer
35
Example 3
There are 45 red balloons and 28 blue balloons in a shop. How many balloons are there in total?
Answer
There are 73 balloons in total.
Always read the word problem carefully to decide if you need to add or subtract.
Common mistakes
- ✗Forgetting to carry over the Ten in addition.
- ✗Forgetting to reduce the Tens digit after borrowing in subtraction.
- ✗Subtracting the smaller digit from the larger digit in the Ones place without regrouping (e.g., subtracting 3 from 8 instead of 8 from 3 after borrowing).
- ✗Not reading word problems carefully and choosing the wrong operation (addition instead of subtraction or vice-versa).
- ✗Not aligning numbers correctly in columns, leading to incorrect calculations.
Exam tips
- ★Practice addition and subtraction with regrouping regularly to become fast and accurate.
- ★In word problems, underline the important numbers and keywords to help you decide the operation.
- ★Always show your working steps clearly, especially for regrouping, as it helps in checking your answer.
- ★After solving a problem, quickly check your answer to ensure it makes sense.
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