What is Finding a Missing Number in Addition?

S0-SA1-1010

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

Finding a missing number in addition means figuring out the unknown value in an addition sum. It's like solving a puzzle where you know the total and one part, and you need to find the other part that completes the sum.

Simple Example

Quick Example

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

Worked Example

Step-by-Step

Let's say a shopkeeper sold 15 packets of biscuits in the morning and some more in the evening. By the end of the day, he had sold a total of 28 packets. How many packets did he sell in the evening?

Step 1: Understand the problem. We know the morning sales (15) and the total sales (28). We need to find the evening sales.
---Step 2: Write it as an addition problem with a missing number: 15 + ? = 28.
---Step 3: To find the missing number, we can use subtraction. Subtract the known part from the total.
---Step 4: Calculation: 28 - 15.
---Step 5: Subtract the ones place: 8 - 5 = 3.
---Step 6: Subtract the tens place: 2 - 1 = 1.
---Step 7: So, 28 - 15 = 13.
---Answer: The shopkeeper sold 13 packets of biscuits in the evening.

Why It Matters

This skill is super important for everyday calculations and problem-solving. It's the foundation for algebra and helps you balance budgets, manage inventory, and even calculate cricket scores. Accountants, shopkeepers, and even data analysts use this basic logic constantly.

Common Mistakes

MISTAKE: Adding the given numbers instead of subtracting. For example, in 5 + ? = 8, students might do 5 + 8. | CORRECTION: Remember that to find a missing 'part' when you know the 'total', you almost always need to subtract the known part from the total.

MISTAKE: Subtracting the total from the known part (e.g., 5 - 8 instead of 8 - 5). | CORRECTION: Always subtract the smaller known number from the larger total when finding a missing addend.

MISTAKE: Not checking the answer. | CORRECTION: After finding the missing number, put it back into the original addition problem to see if it makes sense. For example, if you found 3 for 5 + ? = 8, check if 5 + 3 really equals 8.

Practice Questions

Try It Yourself

QUESTION: You spent ₹25 on a pen and some money on a notebook. If your total bill was ₹40, how much did the notebook cost? | ANSWER: ₹15

QUESTION: In a cricket match, Virat scored 48 runs and Rohit scored some runs. If their total runs were 95, how many runs did Rohit score? | ANSWER: 47 runs

QUESTION: A bus started with 30 passengers. At the first stop, 12 passengers got off, and some new passengers got on. If the bus now has 35 passengers, how many new passengers got on? | ANSWER: 17 passengers

MCQ

Quick Quiz

What number makes the equation true: 7 + ? = 19?

The Correct Answer Is:

To find the missing number, subtract the known part (7) from the total (19). 19 - 7 = 12. So, 7 + 12 = 19.

Real World Connection

In the Real World

When you're checking your mobile data usage, you might see you used 5 GB and have 3 GB left from your monthly plan. To find your total monthly data, you'd add 5 + 3. But if you know your total plan is 10 GB and you've used 7 GB, finding out how much is left (10 - 7) is exactly this concept in action, helping you manage your data plan effectively.

Key Vocabulary

Key Terms

ADDITION: Combining two or more numbers to get a total | MISSING NUMBER: An unknown value in an equation that needs to be found | SUM: The result of an addition problem | ADDEND: A number that is added to another | EQUATION: A mathematical statement showing that two expressions are equal

What's Next

What to Learn Next

Once you're good at finding missing numbers in addition, you can move on to 'Finding Missing Numbers in Subtraction'. This will help you understand how addition and subtraction are related and make you even better at solving number puzzles!