What is a Number Family (of 9)?

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Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A Number Family (like the family of 9) includes all the pairs of numbers that add up to a specific 'target' number. It shows different ways to make that number using addition. For the family of 9, all pairs will sum up to 9.

Simple Example

Quick Example

Imagine you have 9 ladoos. How many different ways can you share them between two friends, say, Rahul and Priya? Rahul could get 1 ladoo and Priya 8 (1+8=9), or Rahul could get 4 and Priya 5 (4+5=9). Each of these pairs (1,8), (4,5) are members of the Number Family of 9.

Worked Example

Step-by-Step

Let's find all the pairs that make up the Number Family of 9.

Step 1: Start with 0. What do you add to 0 to get 9? 0 + 9 = 9. So, (0, 9) is a pair.
---Step 2: Move to 1. What do you add to 1 to get 9? 1 + 8 = 9. So, (1, 8) is a pair.
---Step 3: Move to 2. What do you add to 2 to get 9? 2 + 7 = 9. So, (2, 7) is a pair.
---Step 4: Move to 3. What do you add to 3 to get 9? 3 + 6 = 9. So, (3, 6) is a pair.
---Step 5: Move to 4. What do you add to 4 to get 9? 4 + 5 = 9. So, (4, 5) is a pair.
---Step 6: If you go to 5, you'll get 5 + 4 = 9, which is the same pair as (4, 5) just in a different order. We usually list unique pairs.
---Answer: The Number Family of 9 includes the pairs: (0, 9), (1, 8), (2, 7), (3, 6), and (4, 5).

Why It Matters

Understanding number families helps you quickly solve addition and subtraction problems in your head. It's a foundational skill for mental math, which is useful in daily life like calculating change at a shop or splitting a bill. Cashiers and shopkeepers use mental math constantly!

Common Mistakes

MISTAKE: Forgetting to include 0 in the number family. | CORRECTION: Always start with 0 and the target number itself (e.g., for 9, it's 0+9).

MISTAKE: Repeating pairs in reverse order (e.g., listing both (2,7) and (7,2)). | CORRECTION: While both are correct additions, for a 'family' list, we usually count them as one unique pair (like 2 and 7 are 'friends' in the family). Stop when the numbers start repeating.

MISTAKE: Only thinking of single-digit numbers. | CORRECTION: While number families often start with single digits, any two numbers (including negative numbers or decimals, in higher grades) that sum to the target number belong to the family.

Practice Questions

Try It Yourself

QUESTION: Which pair does NOT belong to the Number Family of 9? (A) 3 and 6, (B) 5 and 4, (C) 2 and 8 | ANSWER: C

QUESTION: If you have 9 rupees and spend 7 rupees, how much do you have left? Which pair from the Number Family of 9 does this problem show? | ANSWER: 2 rupees left. The pair is (7, 2).

QUESTION: Rohan wants to buy a toy that costs 9 rupees. He has one 5-rupee coin and some 1-rupee coins. How many 1-rupee coins does he need to make exactly 9 rupees? Which pair from the Number Family of 9 does this represent? | ANSWER: He needs four 1-rupee coins. The pair is (5, 4).

MCQ

Quick Quiz

Which of these pairs belongs to the Number Family of 9?

1 and 7

2 and 6

3 and 6

4 and 6

The Correct Answer Is:

The Number Family of 9 includes pairs that add up to 9. 3 + 6 = 9, so (3, 6) is a correct pair. The other options do not add up to 9.

Real World Connection

In the Real World

When you're playing traditional Indian board games like Ludo or Snakes and Ladders and need a specific number on the dice to win, you're mentally using number families. For example, if you need to move 9 steps, you might think of combinations like 3+6 or 4+5 if you have two dice. Shopkeepers use this to quickly make change; if something costs Rs 9 and you give Rs 10, they instantly know to return Rs 1.

Key Vocabulary

Key Terms

NUMBER FAMILY: A set of number pairs that add up to a specific target number | PAIR: Two numbers considered together | SUM: The result of adding two or more numbers | TARGET NUMBER: The specific number that all pairs in a family add up to

What's Next

What to Learn Next

Next, you can learn about Number Families for other numbers, like the Number Family of 10 or 20. This will strengthen your addition skills and prepare you for more complex math operations like multiplication and division, which are just fast ways of adding and subtracting!