What is Finding a Missing Number in Addition? | Simple Explanation for Class 5-10

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What is Finding a Missing Number in an Addition?

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

Finding a missing number in an addition means figuring out the unknown number that makes an addition sum correct. You start with a known total and one part, and you need to find the other part that adds up to that total.

Simple Example

Quick Example

Imagine you have 5 laddoos, and your friend gives you some more. Now you have 8 laddoos in total. How many laddoos did your friend give you? This is like finding the missing number in 5 + ? = 8.

Worked Example

Step-by-Step

Let's find the missing number in: 12 + ? = 20

Step 1: Understand the problem. We know one part (12) and the total (20). We need to find the other part.
---Step 2: To find a missing part in addition, we can use subtraction. Subtract the known part from the total.
---Step 3: So, we will calculate 20 - 12.
---Step 4: Perform the subtraction: 20 - 12 = 8.
---Step 5: Check your answer: Does 12 + 8 equal 20? Yes, it does.
---The missing number is 8.

Why It Matters

This basic skill helps you solve problems in daily life, like managing your pocket money or sharing things fairly. It's a foundational concept for algebra and complex problem-solving in fields like engineering and finance, helping you become a smart problem-solver.

Common Mistakes

MISTAKE: Adding the known numbers instead of subtracting. For example, in 5 + ? = 8, students might do 5 + 8 = 13. | CORRECTION: When you know the total and one part, always subtract the known part from the total to find the missing part.

MISTAKE: Subtracting the total from the known part (e.g., 5 - 8 in 5 + ? = 8). | CORRECTION: Always subtract the smaller known part from the larger total to get a positive missing number.

MISTAKE: Forgetting that the missing number could be at the beginning (e.g., ? + 7 = 10). | CORRECTION: The method remains the same: subtract the known part (7) from the total (10) to find the missing number, regardless of its position.

Practice Questions

Try It Yourself

QUESTION: A chaiwala sold 15 cups of tea in the morning. He sold some more in the evening. If he sold 25 cups in total, how many cups did he sell in the evening? | ANSWER: 10 cups

QUESTION: My mom bought a packet of biscuits. My brother ate 6 biscuits, and now there are 18 biscuits left in the packet. How many biscuits were there initially in the packet? (Hint: This is like ? - 6 = 18, which means ? = 18 + 6) | ANSWER: 24 biscuits

QUESTION: You have a target to score 100 runs in a cricket match. You have already scored 45 runs. Your friend helped you score some more, and then you scored another 10 runs by yourself. How many runs did your friend help you score to reach exactly 100 runs? (Think: 45 + friend's runs + 10 = 100) | ANSWER: 45 runs

MCQ

Quick Quiz

What is the missing number in the equation: 23 + ? = 40?

The Correct Answer Is:

To find the missing number, subtract the known number (23) from the total (40). So, 40 - 23 = 17. The other options are incorrect because they either add the numbers or subtract incorrectly.

Real World Connection

In the Real World

When you are checking your monthly mobile data usage, you might see you used 5 GB and have 3 GB left. To find out your total data plan, you'd do 5 + 3 = 8 GB. Or, if you know your plan is 10 GB and you've used 7 GB, you can find out how much is left (10 - 7 = 3 GB). This concept is used in budgeting, inventory management in small shops, and even by delivery apps like Swiggy to calculate total orders.

Key Vocabulary

Key Terms

ADDITION: The process of combining numbers to find a total | SUM: The result of adding two or more numbers | MISSING NUMBER: An unknown value in an equation that needs to be found | EQUATION: A mathematical statement showing that two expressions are equal

What's Next

What to Learn Next

Great job understanding missing numbers in addition! Next, you can explore 'Finding a Missing Number in Subtraction'. This will build on your current skills and show you how subtraction is the opposite of addition, helping you solve even more types of problems.