Addition Problem: Finding the Sum of 3 Units and 9 Units

Basic Addition with Single-Digit Numbers

How many units are there in total if we add 3 units to 9 units?

Remember that the number of units here is the sum of the two amounts.

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

How many units are there in total if we add 3 units to 9 units?

Remember that the number of units here is the sum of the two amounts.

2

Step-by-step solution

To solve this problem, we will follow these steps:

  • Step 1: Identify the numbers given in the problem.
  • Step 2: Use addition to find the sum of these numbers.
  • Step 3: Verify that the sum corresponds to one of the answer choices.

Now, let's work through each step:
Step 1: The problem gives us 3 units and 9 units.
Step 2: We'll use the addition operation.
3+9=12 3 + 9 = 12
Step 3: Check the given choices to ensure our answer, 12, matches one of them.

Therefore, the solution to the problem is 12 12 .

3

Final Answer

12 12

Key Points to Remember

Essential concepts to master this topic
  • Addition Rule: Combine quantities by adding their numerical values together
  • Technique: Count forward from the larger number: start at 9, then +3 = 12
  • Check: Verify by counting units or using subtraction: 12 - 3 = 9 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing addition with other operations
    Don't subtract or multiply when the problem asks to 'add' or find the 'total' = wrong answer! Students sometimes see numbers and automatically use the wrong operation. Always identify the key words like 'add', 'sum', or 'total' to choose addition.

Practice Quiz

Test your knowledge with interactive questions

If we have 67 blocks in total, how many blocks will remain if we remove 5 tens and 4 ones?

FAQ

Everything you need to know about this question

How do I know when to add numbers together?

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Look for key words like 'add', 'sum', 'total', 'altogether', or 'in all'. These signal that you need to combine the numbers using addition!

What's the easiest way to add 3 + 9?

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Start with the larger number (9) and count up by the smaller number (3). So: 9 → 10 → 11 → 12. This counting method helps avoid mistakes!

Can I add in any order?

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Yes! Addition is commutative, which means 3 + 9 gives the same answer as 9 + 3. Both equal 12!

How can I check if my answer is right?

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Try counting backwards from your answer. If 12 is correct, then 12 - 3 should equal 9, and 12 - 9 should equal 3. Both work, so 12 is right!

What if I get confused with word problems?

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Focus on the numbers given and the question asked. Here we have '3 units' and '9 units', and we need the 'total'. That means: 3 + 9 = 12 units.

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