What is Subtracting from 18?

S0-SA1-1304

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

Subtracting from 18 means taking away a certain number from the total of 18. It helps us find out how much is left after a part is removed. This is a basic subtraction operation where 18 is always the starting number.

Simple Example

Quick Example

Imagine you have 18 laddoos in a box. Your friend eats 5 laddoos. To find out how many laddoos are left, you would subtract 5 from 18. This gives you the remaining number of laddoos.

Worked Example

Step-by-Step

Let's subtract 7 from 18.

Step 1: Start with the number 18.

Step 2: We need to take away 7 from 18. This can be written as 18 - 7.

Step 3: You can count backwards 7 steps from 18 (17, 16, 15, 14, 13, 12, 11).

Step 4: Alternatively, you can use column subtraction:
18
- 7
----

Step 5: Subtract the ones place: 8 - 7 = 1.

Step 6: Subtract the tens place: 1 - 0 = 1.

Answer: So, 18 - 7 = 11.

Why It Matters

Understanding 'subtracting from 18' is a building block for all subtraction. It helps you manage money, calculate time, and even understand scores in games like cricket. This skill is crucial for careers in finance, engineering, and even everyday tasks like shopping.

Common Mistakes

MISTAKE: Subtracting the larger number from the smaller number when the smaller number is written first (e.g., trying to do 7 - 18). | CORRECTION: Always subtract the second number from the first number. If it's 'subtracting from 18', then 18 is always the first number.

MISTAKE: Forgetting to borrow when needed in larger subtractions (though not typically for 'from 18'). | CORRECTION: When a digit in the top number is smaller than the digit below it, you need to 'borrow' from the next place value to the left.

MISTAKE: Counting incorrectly when using fingers or mental math. | CORRECTION: Double-check your counting. You can use a number line or draw tally marks to be sure.

Practice Questions

Try It Yourself

QUESTION: A bus has 18 seats. If 9 seats are empty, how many passengers are on the bus? | ANSWER: 18 - 9 = 9 passengers.

QUESTION: You have 18 rupees. You buy a packet of biscuits for 6 rupees. How much money do you have left? | ANSWER: 18 - 6 = 12 rupees.

QUESTION: Your mobile phone battery is at 18%. If it drops by 4% every hour, how much battery will be left after 3 hours? | ANSWER: In 3 hours, it drops 4 x 3 = 12%. So, 18 - 12 = 6% battery left.

MCQ

Quick Quiz

What is the result of subtracting 12 from 18?

The Correct Answer Is:

Subtracting 12 from 18 means 18 - 12. If you count back 12 from 18, you land on 6. So, 6 is the correct answer.

Real World Connection

In the Real World

When you pay for something with a 20-rupee note and the item costs 2 rupees, you expect 18 rupees back. This is similar to subtracting 2 from 20. Or if a cricket team needs 18 runs to win and scores 5 more, they need to subtract 5 from 18 to know the remaining runs needed.

Key Vocabulary

Key Terms

SUBTRACT: To take away one quantity from another | DIFFERENCE: The result of subtracting one number from another | MINUEND: The number from which another number is subtracted (in '18 - X', 18 is the minuend) | SUBTRAHEND: The number being subtracted (in '18 - X', X is the subtrahend)

What's Next

What to Learn Next

Great job understanding subtracting from 18! Now you can move on to 'Subtracting from 20' or 'Subtracting two-digit numbers'. These concepts will build on your current understanding and help you solve even bigger subtraction problems.