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What is 20 - 7?
Grade Level:
Class 2
Maths, Computing, AI
Definition
What is it?
20 - 7 is a simple subtraction problem where you take away 7 from 20. Subtraction helps us find out how much is left after some amount is removed from a total. It's a basic operation to calculate differences.
Simple Example
Quick Example
Imagine you have 20 ladoos for a festival. If your cousins eat 7 of them, how many ladoos are left for you? To find out, you would do 20 - 7.
Worked Example
Step-by-Step
Let's solve 20 - 7 step-by-step:
1. Start with the larger number, which is 20.
2. We need to take away 7 from 20.
3. You can count backwards 7 steps from 20: 20, 19, 18, 17, 16, 15, 14, 13.
4. Alternatively, you can use a number line. Start at 20 and move 7 steps to the left.
5. Another way is to break it down: 20 - 7 = (10 + 10) - 7. Take 7 from one of the 10s: 10 + (10 - 7) = 10 + 3 = 13.
--- The answer is 13.
Why It Matters
Understanding subtraction is crucial for problem-solving in maths and computing. It's used by software developers to manage inventory, by AI engineers to calculate differences in data, and by data scientists to analyze trends. Mastering this skill opens doors to exciting careers in technology.
Common Mistakes
MISTAKE: Subtracting the smaller digit from the larger digit in each place value without borrowing (e.g., in 20-7, thinking 0-7 is 7, and 2-0 is 2, getting 27) | CORRECTION: Always borrow from the tens place when the digit in the ones place is smaller than the digit being subtracted.
MISTAKE: Counting backwards incorrectly or skipping numbers (e.g., 20, 19, 17, 16...) | CORRECTION: Practice counting backwards carefully, step by step, or use physical objects/fingers to ensure accuracy.
MISTAKE: Confusing subtraction with addition (e.g., adding 20 + 7 instead of subtracting) | CORRECTION: Pay close attention to the operation sign (-) which means 'take away' or 'find the difference'.
Practice Questions
Try It Yourself
QUESTION: You had 15 rupees. You bought a small pack of biscuits for 5 rupees. How much money do you have left? | ANSWER: 10 rupees
QUESTION: A bus started with 18 passengers. At the first stop, 6 passengers got off. How many passengers are now on the bus? | ANSWER: 12 passengers
QUESTION: Your favourite cricket team scored 25 runs in the first 3 overs. If they scored 8 runs in the 3rd over, how many runs did they score in the first two overs combined? | ANSWER: 17 runs
MCQ
Quick Quiz
What is the result of 20 - 7?
27
13
17
30
The Correct Answer Is:
B
When you take away 7 from 20, you are left with 13. Options A, C, and D are incorrect results for this subtraction.
Real World Connection
In the Real World
When you check your mobile data balance, and it shows 20 GB remaining, but you use 7 GB for watching videos, your phone's system performs 20 - 7 to show you 13 GB left. This simple subtraction is happening constantly in the apps we use every day, like banking apps (UPI transactions) or e-commerce apps (checking stock).
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: The symbol (-) used to indicate subtraction | REMAINDER: The amount left after subtraction
What's Next
What to Learn Next
Great job with basic subtraction! Next, you can learn about subtracting larger numbers, including borrowing across multiple place values. This will help you solve more complex problems, like calculating change at a shop or managing bigger budgets.
