What is Solving a Number Sentence?

S0-SA1-0292

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

Solving a number sentence means finding the missing number that makes the equation true. It's like a puzzle where you need to figure out what number fits perfectly into the empty space to balance both sides of the sentence.

Simple Example

Quick Example

Imagine you have 5 ladoos, and your friend gives you some more. Now you have 8 ladoos in total. The number sentence is: 5 + ? = 8. To 'solve' it, you need to find out how many ladoos your friend gave you.

Worked Example

Step-by-Step

Let's solve the number sentence: 7 - ? = 4.

Step 1: Understand the problem. We start with 7, take away some number, and are left with 4.
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Step 2: Think about what operation is happening. It's subtraction.
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Step 3: To find the missing number, we can think: 'What do I need to subtract from 7 to get 4?'
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Step 4: Alternatively, we can use the opposite operation (addition). If 7 - ? = 4, then 7 - 4 must be equal to the missing number.
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Step 5: Calculate 7 - 4.
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Step 6: 7 - 4 = 3.
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Step 7: So, the missing number is 3.
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Answer: The missing number is 3. (7 - 3 = 4)

Why It Matters

Solving number sentences is a basic skill that helps you understand algebra and problem-solving in maths. It's crucial for careers like engineers who calculate forces, scientists who balance chemical equations, or even shopkeepers who calculate change.

Common Mistakes

MISTAKE: Always using addition to find the missing number, even in subtraction problems. | CORRECTION: Look carefully at the operation sign (+, -, x, /) and use the inverse operation if needed to find the missing number.

MISTAKE: Guessing the answer instead of using a proper method. | CORRECTION: Use strategies like counting up/down, drawing pictures, or using inverse operations to find the correct answer systematically.

MISTAKE: Not checking the answer by putting it back into the original sentence. | CORRECTION: Once you find a missing number, substitute it back into the number sentence to see if both sides are equal and the sentence is true.

Practice Questions

Try It Yourself

QUESTION: Solve: 12 + ? = 20 | ANSWER: 8

QUESTION: Find the missing number: ? - 6 = 15 | ANSWER: 21

QUESTION: Your mom bought 10 rotis. You ate some, and now there are 7 left. Write and solve the number sentence to find how many rotis you ate. | ANSWER: 10 - ? = 7; The missing number is 3.

MCQ

Quick Quiz

Which of these correctly solves the number sentence: 9 x ? = 36?

The Correct Answer Is:

Option A is correct because 9 multiplied by 4 equals 36. The other options do not make the number sentence true.

Real World Connection

In the Real World

When you are budgeting your pocket money, you often solve number sentences. For example, if you have ₹50 and want to buy a snack for ₹25, you might think: ₹50 - ₹25 = ?. You solve it to find out how much money you have left.

Key Vocabulary

Key Terms

NUMBER SENTENCE: An equation with numbers and an operation, often with a missing value | MISSING NUMBER: The unknown value in a number sentence that needs to be found | SOLVE: To find the answer or the missing value in a problem | EQUATION: A statement that two mathematical expressions are equal

What's Next

What to Learn Next

Now that you can solve basic number sentences, you're ready to learn about 'Introduction to Variables'. This is where you'll use letters like 'x' or 'y' instead of question marks to represent missing numbers, which is the first step into algebra!