What is a Number Bond to 20?

S0-SA1-0033

Grade Level:

Class 1

Maths

Definition

What is it?

A Number Bond to 20 shows how two smaller numbers add up to make the number 20. It's like finding pairs of numbers that complete 20 when put together. Understanding number bonds helps you quickly see parts that make a whole.

Simple Example

Quick Example

Imagine you have 20 cricket balls. If your friend takes 8 balls, how many balls are left with you? The number bond to 20 helps us see that 8 + 12 = 20. So, 12 balls are left.

Worked Example

Step-by-Step

Let's find the missing number in the bond: 15 + ? = 20.

Step 1: Start with the total, which is 20.
---Step 2: We know one part is 15.
---Step 3: To find the missing part, we subtract the known part from the total: 20 - 15.
---Step 4: Count back 15 from 20 (20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5).
---Step 5: The answer is 5.

So, 15 + 5 = 20. The missing number is 5.

Why It Matters

Understanding number bonds is super important for quick mental maths and solving problems faster. It's used by shopkeepers to calculate change, by engineers to balance loads, and by data scientists to split information into groups.

Common Mistakes

MISTAKE: Adding the two given numbers instead of finding the missing part. For example, for 7 + ? = 20, students might add 7 + 20. | CORRECTION: Remember that 20 is the total. You need to find the number that, when added to the given number, reaches 20.

MISTAKE: Confusing number bonds to 20 with number bonds to 10 or other numbers. | CORRECTION: Always check the 'target' number. For number bonds to 20, the sum must always be exactly 20.

MISTAKE: Not being able to quickly recall common bonds like 10 + 10 or 5 + 15. | CORRECTION: Practice recalling these pairs often. Flashcards or simple games can help you memorise them for faster calculations.

Practice Questions

Try It Yourself

QUESTION: What number completes the bond: 6 + ? = 20? | ANSWER: 14

QUESTION: A bus has 20 seats. If 13 seats are already taken, how many seats are empty? | ANSWER: 7

QUESTION: You need 20 rupees to buy a snack. You have a 10 rupee coin and a 5 rupee coin. How much more money do you need? | ANSWER: 5 rupees

MCQ

Quick Quiz

Which pair of numbers makes a number bond to 20?

7 and 10

8 and 12

9 and 9

15 and 4

The Correct Answer Is:

The correct option is B because 8 + 12 equals 20. Options A, C, and D do not add up to 20.

Real World Connection

In the Real World

When you pay for something with a 20-rupee note at a small shop, the shopkeeper quickly calculates your change using number bonds. For example, if your item costs 7 rupees, they know 7 + 13 = 20, so they return 13 rupees to you instantly.

Key Vocabulary

Key Terms

NUMBER BOND: Two numbers that add up to a specific total | SUM: The result of adding two or more numbers | TOTAL: The whole amount or final number | PAIR: Two of something

What's Next

What to Learn Next

Great job learning about Number Bonds to 20! Next, you can explore 'Number Bonds to 100' or 'Addition and Subtraction within 100'. These build on what you've learned to help you work with larger numbers more confidently.