What is a Number Family of 8?

S0-SA1-1244

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A Number Family of 8 includes all the addition and subtraction facts that use the numbers 8, and two other numbers that add up to 8. It shows how these three numbers are related through addition and subtraction.

Simple Example

Quick Example

Imagine you have 8 ladoos. If your friend eats 3 ladoos, you are left with 5. This shows 8 - 3 = 5. Also, if you had 3 ladoos and your friend gave you 5 more, you'd have 8 (3 + 5 = 8). The numbers 3, 5, and 8 form a 'ladoo family' for 8!

Worked Example

Step-by-Step

Let's find the number family for 8 using the numbers 2 and 6.

1. First, check if 2 and 6 add up to 8: 2 + 6 = 8. Yes, they do!
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2. Write the first addition fact: 2 + 6 = 8.
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3. Now, reverse the numbers for the second addition fact: 6 + 2 = 8.
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4. For subtraction, start with the largest number (8) and subtract one of the smaller numbers: 8 - 2 = 6.
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5. Finally, subtract the other smaller number from 8: 8 - 6 = 2.
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So, the number family for 8 using 2 and 6 is: 2 + 6 = 8, 6 + 2 = 8, 8 - 2 = 6, and 8 - 6 = 2.

Why It Matters

Understanding number families helps you solve math problems faster and makes mental math much easier. It's like knowing shortcuts! This skill is crucial for careers in finance, like a bank manager managing money, or even for engineers calculating materials needed for a building.

Common Mistakes

MISTAKE: Only writing addition facts and forgetting subtraction facts. | CORRECTION: Remember that a number family always includes two addition and two subtraction facts.

MISTAKE: Using numbers that don't add up to the target number (8 in this case). For example, saying 3 and 4 are a family of 8. | CORRECTION: Always check that the two smaller numbers sum up to the main number (e.g., 3 + 4 = 7, not 8).

MISTAKE: Mixing up the numbers in subtraction, like writing 2 - 8 = 6. | CORRECTION: In subtraction for a number family, always start with the largest number (8) and subtract one of the smaller numbers.

Practice Questions

Try It Yourself

QUESTION: Which two numbers from this list form a number family of 8: 1, 3, 5, 7? | ANSWER: 1 and 7 (because 1 + 7 = 8)

QUESTION: Write all four facts for the number family of 8 using the numbers 4 and 4. | ANSWER: 4 + 4 = 8, 8 - 4 = 4 (Note: Since both numbers are the same, there are only two unique facts)

QUESTION: If you have 8 rupees and spend 5 rupees on a chai, what number family facts can you make with 8, 5, and the amount left? | ANSWER: You have 3 rupees left (8 - 5 = 3). The facts are: 5 + 3 = 8, 3 + 5 = 8, 8 - 5 = 3, 8 - 3 = 5.

MCQ

Quick Quiz

Which set of facts correctly shows a number family of 8 using the numbers 7 and 1?

7 + 1 = 8, 1 + 7 = 8, 8 - 7 = 1, 8 - 1 = 7

7 + 1 = 8, 8 - 7 = 1, 7 - 1 = 6, 8 + 1 = 9

7 + 1 = 8, 1 + 7 = 8, 7 - 1 = 6, 1 - 7 = -6

7 + 1 = 8, 8 - 1 = 7, 7 + 2 = 9, 8 - 2 = 6

The Correct Answer Is:

Option A correctly shows all four related addition and subtraction facts (two addition, two subtraction) that use the numbers 7, 1, and 8. The other options either include incorrect facts or miss some facts.

Real World Connection

In the Real World

When a shopkeeper gives you change after you buy something, they are using number families! For example, if an item costs 3 rupees and you give them an 8-rupee note, they quickly calculate 8 - 3 = 5 rupees change. This quick calculation is based on understanding number families.

Key Vocabulary

Key Terms

Number Family: A set of related addition and subtraction facts using three numbers | Addition Fact: A mathematical statement showing two numbers added together to get a sum | Subtraction Fact: A mathematical statement showing one number taken away from another to find the difference | Sum: The result of adding two or more numbers | Difference: The result of subtracting one number from another.

What's Next

What to Learn Next

Great job learning about the Number Family of 8! Now you're ready to explore 'Number Families for other numbers like 9 or 10'. The same rules apply, just with different numbers, which will make your addition and subtraction skills even stronger!