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

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What is a Missing Number in an Addition?

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A missing number in an addition problem is a number that is not given but is needed to complete the sum correctly. It's like a puzzle where you have some parts of the addition equation, and you need to find the missing piece to make it true.

Simple Example

Quick Example

Imagine you have 5 cricket balls, and your friend gives you some more. Now you have a total of 8 cricket balls. How many balls did your friend give you? Here, the number of balls your friend gave you is the missing number in the addition: 5 + ? = 8.

Worked Example

Step-by-Step

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

1. Identify the known numbers: We know one part is 12 and the total sum is 20.
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2. Understand the goal: We need to find the number that, when added to 12, gives us 20.
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3. Think of it as subtraction: To find the missing part, you can subtract the known part from the total sum.
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4. Perform the subtraction: 20 - 12
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5. Calculate the result: 20 - 12 = 8
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6. Check your answer: Substitute the missing number back into the original problem: 12 + 8 = 20. This is correct.

So, the missing number is 8.

Why It Matters

Understanding missing numbers helps you solve problems in daily life, like managing your pocket money or splitting bills. This skill is fundamental for careers in finance, data analysis, and even shopkeeping, where you constantly deal with quantities and totals.

Common Mistakes

MISTAKE: Adding the known numbers together instead of subtracting. For example, in 5 + ? = 8, students might do 5 + 8 = 13. | CORRECTION: Remember that the missing number is a 'part' of the total. To find a missing part when you know the total and one part, you must subtract the known part from the total.

MISTAKE: Confusing the position of the missing number. For example, thinking ? + 3 = 7 is different from 3 + ? = 7. | CORRECTION: In addition, the order of numbers doesn't change the sum (commutative property). So, finding the missing number works the same way regardless of its position.

MISTAKE: Not checking the answer. Students find a number and move on without verifying. | CORRECTION: Always substitute your found missing number back into the original equation to ensure it makes the statement true. This simple check prevents many errors.

Practice Questions

Try It Yourself

QUESTION: Your mom gave you Rs. 15, and you want to buy a toy car that costs Rs. 25. How much more money do you need? (15 + ? = 25) | ANSWER: Rs. 10

QUESTION: In a class of 30 students, 18 are boys. How many girls are there? (18 + ? = 30) | ANSWER: 12 girls

QUESTION: A delivery driver has to deliver 50 parcels. He delivered 23 in the morning and some more in the afternoon. By evening, he had 5 parcels left to deliver. How many parcels did he deliver in the afternoon? (23 + ? + 5 = 50) | ANSWER: 22 parcels

MCQ

Quick Quiz

Which operation would you use to find the missing number in 7 + ? = 15?

Addition

Subtraction

Multiplication

Division

The Correct Answer Is:

To find a missing number in an addition problem where the sum is known, you subtract the known addend from the sum. So, 15 - 7 will give the missing number.

Real World Connection

In the Real World

When you use a digital payment app like PhonePe or Google Pay to split a bill with friends at a restaurant, you might see that the total is Rs. 500, and your friend paid Rs. 200. To figure out how much you still need to pay, you're essentially solving a missing number problem: 200 + ? = 500.

Key Vocabulary

Key Terms

ADDITION: The process of combining numbers to find their total | SUM: The total amount resulting from adding two or more numbers | MISSING NUMBER: A value that is unknown and needs to be found to complete an equation | EQUATION: A mathematical statement that shows two expressions are equal

What's Next

What to Learn Next

Great job understanding missing numbers in addition! Next, you can explore 'Missing Numbers in Subtraction'. This will build on your current knowledge and help you solve even more complex everyday problems.