Subtraction trick you need to know

🧮 Subtraction and Tricks – Lecture Notes

1. What is Subtraction?

• Subtraction means taking away one number from another.

• It tells us how much is left or the difference between two numbers.

Example:
8 – 5 = 3 → We took away 5 from 8, 3 is left.

2. Subtraction Vocabulary

3. Subtraction with Borrowing (Regrouping)

When a smaller digit is on top and a larger one below, we borrow from the next column.

Example:

Step 1: Borrow 1 from the tens → 12 – 8 = 4
Step 2: Now tens become 4 → 4 – 3 = 1
✅ Answer: 14

4. Left-to-Right Subtraction Trick

Normally, we subtract from right to left. But here’s a faster method for mental maths:

Example:
643 – 321
→ (600 – 300) + (40 – 20) + (3 – 1)
→ 300 + 20 + 2 = ✅ 322

This method helps do subtraction mentally without borrowing!

5. Subtracting Using Complements

Use the idea of “making 10” or “complement” to subtract easily.

Example:
1000 – 673
Think:
(1000 – 700) + (700 – 673) = 300 + 27 = ✅ 327

Trick: Subtract each digit from 9, except the last one from 10!
→ 1000 – 673 = (9–6)(9–7)(10–3) = ✅ 327

6. Subtraction Trick Without Borrowing

When borrowing confuses you, adjust both numbers slightly to make subtraction easier.

Example:
502 – 298
Add 2 to both → 504 – 300 = ✅ 204

This avoids messy borrowing!

7. Checking Your Answer

Always add the difference to the subtrahend.
If it equals the minuend, your answer is correct!

Example:
84 – 59 = 25
Check → 25 + 59 = ✅ 84

8. Practice Tips

✅ Line up numbers correctly (units under units, tens under tens).
✅ Use mental subtraction for simple numbers.
✅ Apply tricks to save time in competitive exams.