What is 20 - 7? | Simple Explanation for Class 2

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What is 20 - 7?

Grade Level:

Class 2

Maths, Computing, AI

Definition

What is it?

20 - 7 means taking away 7 from 20. It's a basic subtraction problem where you find the difference between two numbers. This helps you figure out how much is left after some amount is removed.

Simple Example

Quick Example

Imagine you have 20 ladoos for a festival. If your friends eat 7 ladoos, how many ladoos are left for you? To find this, you do 20 - 7.

Worked Example

Step-by-Step

Let's find the answer to 20 - 7:

1. Start with the number 20.
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2. We need to take away 7 from 20.
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3. You can count backwards 7 steps from 20: 19, 18, 17, 16, 15, 14, 13.
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4. Alternatively, you can think of it as breaking down 20 into 10 + 10. Take 7 from one of the 10s (10 - 7 = 3).
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5. Now add that 3 to the other 10 (10 + 3 = 13).
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6. So, when you take 7 away from 20, you are left with 13.
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Answer: 13

Why It Matters

Understanding subtraction is crucial for everyday problem-solving and forms the base for advanced maths, computing, and AI. Engineers use it to calculate material differences, programmers use it in coding logic, and data scientists use it to compare data sets and find trends.

Common Mistakes

MISTAKE: Writing 7 - 20 instead of 20 - 7 | CORRECTION: Always subtract the smaller number from the larger number unless specified otherwise, and the first number is what you start with.

MISTAKE: Counting incorrectly, like skipping a number when counting backwards | CORRECTION: Double-check your counting. You can use fingers, tally marks, or a number line to be sure.

MISTAKE: Getting confused with place values in bigger numbers | CORRECTION: For single-digit subtraction from a two-digit number, remember you are only taking from the 'ones' place if it's large enough, or 'borrowing' from the 'tens' place.

Practice Questions

Try It Yourself

QUESTION: You have 15 cricket balls. If 6 balls get lost, how many are left? | ANSWER: 9

QUESTION: A bus has 22 passengers. At the next stop, 8 passengers get down. How many passengers are still on the bus? | ANSWER: 14

QUESTION: Your mom bought a pack of 30 biscuits. You ate 5, and your sister ate 4. How many biscuits are left? | ANSWER: 21

MCQ

Quick Quiz

What is the result of 18 - 5?

The Correct Answer Is:

18 minus 5 means taking 5 away from 18. If you count back 5 from 18 (17, 16, 15, 14, 13), you get 13. So, option B is correct.

Real World Connection

In the Real World

When you check your mobile data balance, you often see how much data you started with and how much you've used. To find out how much data is left for the day, your phone's system performs a subtraction, like 2 GB (total) - 0.5 GB (used) = 1.5 GB (remaining).

Key Vocabulary

Key Terms

SUBTRACTION: The process of taking one number or quantity away from another | DIFFERENCE: The result of subtracting one number from another | MINUS: A symbol (-) used to show subtraction | QUANTITY: An amount or number of something

What's Next

What to Learn Next

Great job understanding basic subtraction! Next, you can explore subtraction with larger numbers and learn about borrowing. This will help you solve even more complex everyday problems.