What is a Number Family? | Simple Explanation for Class 1-2

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What is a Number Family (of 13)?

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A 'Number Family' (of 13 in this case) is a group of related math facts that use the same three numbers. These facts usually involve addition and subtraction, showing how the numbers are connected. For example, in the family of 13, the numbers 5, 8, and 13 are related because 5 + 8 = 13.

Simple Example

Quick Example

Imagine you have 13 laddus. If your friend eats 5 laddus, you are left with 8 laddus (13 - 5 = 8). Or, if you have 5 laddus and your friend gives you 8 more, you now have 13 laddus (5 + 8 = 13). The numbers 5, 8, and 13 form a family because they are all part of these sweet calculations.

Worked Example

Step-by-Step

Let's find the Number Family for 13 using the numbers 6 and 7.
1. We start with the idea that two smaller numbers add up to the biggest number. So, 6 + 7 = 13.
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2. Since addition is commutative (meaning the order doesn't change the sum), we can also write 7 + 6 = 13.
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3. Now, let's use subtraction. If we take the biggest number (13) and subtract one of the smaller numbers (6), we should get the other smaller number: 13 - 6 = 7.
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4. Similarly, if we take the biggest number (13) and subtract the other smaller number (7), we should get the first smaller number: 13 - 7 = 6.
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Answer: The Number Family of 13 for 6 and 7 includes: 6 + 7 = 13, 7 + 6 = 13, 13 - 6 = 7, and 13 - 7 = 6.

Why It Matters

Understanding number families helps you solve math problems faster and makes mental calculations easier. This concept is fundamental for understanding algebra, where you find missing numbers, and in fields like finance, where you balance budgets. Even engineers use these basic relationships to calculate forces and measurements.

Common Mistakes

MISTAKE: Only writing addition facts for a number family. | CORRECTION: Remember to include all related subtraction facts as well. A complete family has both.

MISTAKE: Using numbers that don't actually add up to the 'family' number. For example, saying 4, 8, and 13 are a family because 4 + 8 = 12, not 13. | CORRECTION: Always check that the two smaller numbers correctly add up to the largest number in the family.

MISTAKE: Confusing the biggest number with one of the smaller numbers in subtraction. For instance, writing 6 - 13 = 7. | CORRECTION: In subtraction for a number family, you always start with the largest number (the sum) and subtract one of the smaller numbers.

Practice Questions

Try It Yourself

QUESTION: Write the number family for 10 using the numbers 3 and 7. | ANSWER: 3 + 7 = 10, 7 + 3 = 10, 10 - 3 = 7, 10 - 7 = 3

QUESTION: If 15 is the biggest number in a family, and one smaller number is 9, what is the other smaller number? Write the full family. | ANSWER: The other number is 6 (because 15 - 9 = 6). The family is: 9 + 6 = 15, 6 + 9 = 15, 15 - 9 = 6, 15 - 6 = 9.

QUESTION: Ram bought a cricket bat for Rs 800 and a ball for Rs 200. The total amount he spent is Rs 1000. Form the number family using these three numbers. | ANSWER: 800 + 200 = 1000, 200 + 800 = 1000, 1000 - 800 = 200, 1000 - 200 = 800.

MCQ

Quick Quiz

Which set of facts correctly represents a Number Family for 12, using the numbers 5 and 7?

5 + 7 = 12, 12 - 5 = 7, 7 - 5 = 2

5 + 7 = 12, 7 + 5 = 12, 12 - 5 = 7, 12 - 7 = 5

5 + 7 = 12, 12 - 7 = 5, 5 + 12 = 17

7 + 5 = 12, 12 + 5 = 17, 12 - 7 = 5

The Correct Answer Is:

Option B includes all four correct facts: two addition facts (5+7=12, 7+5=12) and two subtraction facts (12-5=7, 12-7=5) using only the numbers 5, 7, and 12. Other options include incorrect operations or unrelated numbers.

Real World Connection

In the Real World

When you're checking your monthly mobile data usage, you might see you used 8 GB out of a 15 GB plan. To quickly find out how much data is left (7 GB), you're using a number family (15 - 8 = 7). Similarly, shopkeepers use number families to quickly calculate change when a customer pays, like if an item costs Rs 45 and the customer gives Rs 100, they know to return Rs 55 (100 - 45 = 55).

Key Vocabulary

Key Terms

ADDITION: Combining two or more numbers to find a total | SUBTRACTION: Taking one number 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 number families! Next, you can explore 'Fact Families with Multiplication and Division.' This will show you how the same concept applies to multiplication and division, making you even better at understanding number relationships.