What is a Number Family of 15?

S0-SA1-1249

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

A 'Number Family' for a specific number like 15 includes all the pairs of whole numbers that add up to that number. It helps us understand different ways to make a total using addition.

Simple Example

Quick Example

Imagine you have 15 ladoos for a festival. You want to share them with your friend. How many can you give your friend and how many can you keep? You could keep 10 and give 5 (10 + 5 = 15), or keep 7 and give 8 (7 + 8 = 15). Each pair (10, 5) or (7, 8) is part of the 'Number Family of 15'.

Worked Example

Step-by-Step

Let's find all the pairs in the Number Family of 15.

1. Start with 0: 0 + ? = 15. So, 0 + 15 = 15. (Pair: 0, 15)
---2. Move to 1: 1 + ? = 15. So, 1 + 14 = 15. (Pair: 1, 14)
---3. Move to 2: 2 + ? = 15. So, 2 + 13 = 15. (Pair: 2, 13)
---4. Continue this pattern: 3 + 12 = 15 (Pair: 3, 12)
---5. 4 + 11 = 15 (Pair: 4, 11)
---6. 5 + 10 = 15 (Pair: 5, 10)
---7. 6 + 9 = 15 (Pair: 6, 9)
---8. 7 + 8 = 15 (Pair: 7, 8)

The Number Family of 15 includes these pairs: (0, 15), (1, 14), (2, 13), (3, 12), (4, 11), (5, 10), (6, 9), (7, 8).

Why It Matters

Understanding number families builds a strong foundation for addition and subtraction, making mental math much faster. This skill is crucial for everyday tasks like calculating change at a shop or budgeting money. It's also used by shopkeepers, cashiers, and even game developers who need to manage scores or resources.

Common Mistakes

MISTAKE: Forgetting to include pairs where one number is 0. For example, only listing pairs like (1, 14), (2, 13) and so on. | CORRECTION: Always start with 0 + the number itself, as (0, 15) is a valid pair in the number family.

MISTAKE: Listing the same pair twice, like (1, 14) and then (14, 1). | CORRECTION: While 1 + 14 and 14 + 1 both equal 15, they represent the same pair of numbers for the family. List each unique pair only once, usually by keeping the first number smaller or equal to the second.

MISTAKE: Including pairs that do not add up to the target number. For example, listing (6, 8) for the number family of 15. | CORRECTION: Double-check each pair by adding the two numbers together to ensure their sum is exactly the target number (15 in this case).

Practice Questions

Try It Yourself

QUESTION: Which of these pairs belongs to the Number Family of 15? (A) (7, 7) (B) (8, 7) (C) (9, 5) | ANSWER: (B) (8, 7) because 8 + 7 = 15.

QUESTION: List all the pairs in the Number Family of 10. | ANSWER: (0, 10), (1, 9), (2, 8), (3, 7), (4, 6), (5, 5).

QUESTION: Rohit has 15 marbles. He wants to put them into two boxes. List all the different ways he can divide the marbles between the two boxes. | ANSWER: (0, 15), (1, 14), (2, 13), (3, 12), (4, 11), (5, 10), (6, 9), (7, 8). These are all the pairs in the Number Family of 15.

MCQ

Quick Quiz

Which of these pairs is NOT part of the Number Family of 15?

(5, 10)

(6, 9)

(7, 8)

(4, 9)

The Correct Answer Is:

The correct answer is (D) because 4 + 9 = 13, not 15. All other options add up to 15.

Real World Connection

In the Real World

When you are playing cricket and your team needs 15 runs to win, how can the batsmen score those runs? They could hit a 6 and a 4 and a 5 (6+4+5=15), or three 5s (5+5+5=15). Understanding number families helps quickly figure out different combinations to reach a target score. Similarly, when a tailor has a 15-meter cloth, they use number families to decide how much cloth to use for different garments.

Key Vocabulary

Key Terms

NUMBER FAMILY: A set of pairs of numbers that add up to a specific total | PAIR: Two numbers considered together | SUM: The result of adding two or more numbers | WHOLE NUMBERS: Numbers without fractions or decimals (0, 1, 2, 3, ...)

What's Next

What to Learn Next

Now that you understand number families for addition, you can explore how they connect to subtraction. Knowing that 5 + 10 = 15 also means 15 - 5 = 10 and 15 - 10 = 5. This will make you a master of basic arithmetic!