For Class 5 students preparing for competitive exams like the International Mathematics Olympiad (IMO), speed is just as important as accuracy. Knowing a few smart mental math tricks can easily cut calculation time in half.
In this guide, we will explore some of the best mathematical shortcuts that are easy to learn and highly effective during exams.
Instead of relying entirely on rough sheets, building strong mental math reflexes allows you to save crucial minutes, giving you more time to tackle the high-weightage Achievers Section.
1. The Magic of Multiplying by 11
Multiplying a two-digit number by 11 doesn't require a rough sheet. You can do it in your head in seconds.
- Take the original number and imagine a space between its two digits. (e.g., 53 → 5 _ 3)
- Add the two digits together. (5 + 3 = 8)
- Place the sum in the middle. (5 8 3)
Answer: 53 × 11 = 583.
2. Squaring Numbers Ending in 5
Need to square 35, 45, or 85 quickly? Here is a foolproof trick that works every time.
If you need to square 65:
- Take the first digit (6).
- Multiply it by the next highest number (6 × 7 = 42).
- Just append "25" to the end of your result.
Answer: 65² = 4225.
This works seamlessly for any two-digit number ending in 5. Try it with 35: (3 × 4 = 12), append 25 → 1225.
3. Rapid Division by 5
Dividing a large number by 5 can be tedious. Instead, use this two-step shortcut:
- Step 1: Multiply the entire number by 2.
- Step 2: Move the decimal point one place to the left.
Example: 435 ÷ 5
Step 1: 435 × 2 = 870.
Step 2: Move the decimal → 87.0.
4. Multiplying any Number by 9, 99, or 999
This is a fantastic trick for larger calculations that look intimidating at first glance. To multiply a number by 99:
- Add two zeros to the end of the original number (essentially multiplying by 100).
- Subtract the original number from this new value.
Example: 45 × 99
Step 1: 4500
Step 2: 4500 - 45 = 4455.
Start Practicing Now
Knowing these tricks is only half the battle; the real mastery comes from applying them in high-pressure situations. Practice these shortcuts using our timed Olympiad mock tests to see a visible jump in your scores.
Remember, mathematics is a skill, not just a subject. The more you play with numbers, the more intuitive these shortcuts will become!