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What is 20 - 9?
Grade Level:
Class 2
Maths, Computing, AI
Definition
What is it?
20 - 9 means taking away 9 from 20. It is a subtraction problem where you start with 20 items and remove 9 of them to find out how many are left.
Simple Example
Quick Example
Imagine you have 20 ladoos for a festival. If your family eats 9 of them, how many ladoos are left for you? To find out, you calculate 20 - 9.
Worked Example
Step-by-Step
Let's find out what 20 - 9 is: --- Step 1: Start with the larger number, which is 20. --- Step 2: We need to subtract 9 from 20. You can count backwards 9 times from 20. --- Step 3: 20 - 1 = 19 --- Step 4: 19 - 1 = 18 --- Step 5: ...and so on, until you have subtracted 9 times. (Or, you can think: 20 is 10 + 10. If you take away 9 from one of the 10s, you get 1. So 10 + 1 = 11.) --- Step 6: Counting back 9 times from 20: 19, 18, 17, 16, 15, 14, 13, 12, 11. --- Answer: 20 - 9 = 11.
Why It Matters
Understanding basic subtraction like 20 - 9 is crucial for higher Maths, Computing, and even AI. It's the foundation for solving complex equations, managing data in computers, and even for AI programs that make decisions based on numerical differences. Careers in data science, software development, and robotics all use these basic operations constantly.
Common Mistakes
MISTAKE: Students sometimes subtract the larger digit from the smaller digit when numbers are stacked, like 9 from 0 in the ones place. | CORRECTION: Always subtract the bottom number from the top number. If the top digit is smaller, you need to 'borrow' from the tens place.
MISTAKE: Counting backwards incorrectly or missing a number. For example, counting 20, 19, 18, 17, 16, 15, 14, 13, 12 (which is 9 steps, but stops at 12). | CORRECTION: Be very careful while counting backwards. Start counting '1' for the first number you say after the starting number. So, from 20, the first count is 19 (1), then 18 (2), and so on.
MISTAKE: Confusing subtraction with addition. Thinking 20 - 9 is 29. | CORRECTION: Remember, the minus sign (-) means 'take away' or 'find the difference'. The answer should always be smaller than the starting number (20 in this case).
Practice Questions
Try It Yourself
QUESTION: You had 15 rupees and spent 5 rupees on a small packet of biscuits. How much money do you have left? | ANSWER: 10 rupees
QUESTION: A cricket team scored 28 runs in an over. If 7 runs were from boundaries (fours and sixes), how many runs were scored by running between the wickets? | ANSWER: 21 runs
QUESTION: Your school library has 30 storybooks. If 12 books are borrowed today and 5 new books are added tomorrow, how many storybooks will be in the library then? (Hint: first subtract, then add) | ANSWER: 23 books
MCQ
Quick Quiz
What is the result of 20 - 9?
10
11
12
29
The Correct Answer Is:
B
Subtracting 9 from 20 means taking 9 away from 20. Counting back 9 steps from 20 (20-1=19, 19-1=18, ... up to 11) gives 11. Options A, C, and D are incorrect.
Real World Connection
In the Real World
Subtraction is used every day! When you check your mobile data balance, if you started with 2 GB and used 0.5 GB, you subtract to see what's left. When a shopkeeper gives you change after you buy something, they are doing subtraction. Even a delivery app like Swiggy or Zomato uses subtraction to calculate how much time is left until your food arrives.
Key Vocabulary
Key Terms
SUBTRACTION: Taking one number away from another to find the difference | MINUS SIGN (-): The symbol used for subtraction | DIFFERENCE: The result of a subtraction problem | COUNTING BACKWARDS: A strategy for subtraction where you count down from the larger number | ONES PLACE: The rightmost digit in a number, representing single units.
What's Next
What to Learn Next
Great job mastering basic subtraction! Next, you can learn about 'Subtraction with Borrowing' for larger numbers. This will help you subtract numbers like 45 - 18, which builds directly on what you've learned here.
