What is a Number Family for 7?

S0-SA1-1219

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A number family for a specific number, like 7, includes all the addition and subtraction facts that use the same three numbers. It shows how these three numbers are related through addition and subtraction. For example, if 3, 4, and 7 are in a family, you can make two addition facts and two subtraction facts.

Simple Example

Quick Example

Imagine you have 7 laddoos. If you eat 3 laddoos, you have 4 left. This means 7 - 3 = 4. This also tells us that if you had 3 laddoos and got 4 more, you'd have 7 in total (3 + 4 = 7). So, 3, 4, and 7 form a number family.

Worked Example

Step-by-Step

Let's find the number family for 7 using the numbers 5 and 2.
1. Identify the three numbers: 5, 2, and 7.
2. Write the first addition fact: Start with the two smaller numbers. 5 + 2 = 7.
3. Write the second addition fact: Swap the order of the two smaller numbers. 2 + 5 = 7.
4. Write the first subtraction fact: Start with the largest number and subtract one of the smaller numbers. 7 - 5 = 2.
5. Write the second subtraction fact: Start with the largest number and subtract the other smaller number. 7 - 2 = 5.
So, the number family for 7 using 5 and 2 is: 5 + 2 = 7, 2 + 5 = 7, 7 - 5 = 2, and 7 - 2 = 5.

Why It Matters

Understanding number families helps you solve math problems faster and build a strong foundation for bigger numbers. This concept is crucial for everyday calculations, like managing money or understanding cricket scores. It's used by shopkeepers, accountants, and even game developers!

Common Mistakes

MISTAKE: Using numbers that don't add up to the target number (e.g., for 7, using 3 and 5 instead of 3 and 4). | CORRECTION: Always ensure the two smaller numbers add up to the largest number in the family.

MISTAKE: Forgetting to write all four facts (two addition, two subtraction). | CORRECTION: Remember that a complete number family always has four facts, showing all possible relationships between the three numbers.

MISTAKE: In subtraction facts, not starting with the largest number. | CORRECTION: Subtraction facts in a number family always begin with the largest number, from which you subtract one of the smaller numbers.

Practice Questions

Try It Yourself

QUESTION: Which number is missing in this family for 7: 4, 3, __? | ANSWER: 7

QUESTION: Write the complete number family for 7 using the numbers 1 and 6. | ANSWER: 1 + 6 = 7, 6 + 1 = 7, 7 - 1 = 6, 7 - 6 = 1

QUESTION: If a shopkeeper sells 7 packets of biscuits today and 2 of them were 'choco-chip', how many were not 'choco-chip'? Use this information to write one addition and one subtraction fact from the number family for 7. | ANSWER: 7 - 2 = 5 (5 packets were not choco-chip). 5 + 2 = 7 (addition fact).

MCQ

Quick Quiz

Which set of facts correctly shows a number family for 7 using 3 and 4?

3 + 4 = 7, 4 + 3 = 7, 7 - 3 = 4, 7 - 4 = 3

3 + 4 = 7, 7 - 3 = 4, 4 - 3 = 1, 7 + 3 = 10

3 + 7 = 10, 4 + 3 = 7, 7 - 4 = 3, 7 - 3 = 4

7 - 4 = 3, 7 - 3 = 4, 3 + 4 = 7, 4 + 7 = 11

The Correct Answer Is:

Option A correctly shows all four related addition and subtraction facts using only the numbers 3, 4, and 7. The other options include incorrect facts or numbers not belonging to the family.

Real World Connection

In the Real World

When you're sharing 7 pieces of pakora with your friend, and you take 3, you know your friend gets 4 without even counting, because 3 + 4 = 7. Similarly, if your mobile data plan gives you 7 GB and you've used 2 GB, you instantly know you have 5 GB left (7 - 2 = 5). This simple math helps you manage things every day!

Key Vocabulary

Key Terms

ADDITION: Putting numbers together to find a total | SUBTRACTION: Taking one number away from another | NUMBER FAMILY: A set of related addition and subtraction facts using the same three numbers | FACT: A true mathematical statement

What's Next

What to Learn Next

Great job understanding number families! Next, you can explore number families for larger numbers, like 10 or 20. This will help you become even better at mental math and prepare you for more complex addition and subtraction problems.