Rj Gaurav garg

The 9 Multiplication Finger Trick

It works for multiplying any number by 9.

👉 Example: 9 × 7
1. Hold out both hands (10 fingers).
2. Count to the 7th finger from the left and bend it down.
3. Fingers to the left of the bent one = 6
4. Fingers to the right of the bent one = 3
5. Put them together → 63 ✅

So, 9 × 7 = 63.

🎩 The 1089 Trick
1. Think of any 3-digit number where the first and last digits are different (e.g., 732).
2. Reverse the digits (e.g., 237).
3. Subtract the smaller number from the larger (732 – 237 = 495).
4. Now reverse this result (495 → 594).
5. Add them together → 495 + 594 = 1089 🎉

👉 No matter what number you start with, you’ll always end up with 1089!

Solve

29 September in Math History
1. Gauss’s Disquisitiones Arithmeticae published
On 29 September 1801, Carl Friedrich Gauss’s magnum opus Disquisitiones Arithmeticae was published. 
• Gauss had written much of it earlier (when he was ~21). 
• This work laid foundations for number theory: congruences, quadratic reciprocity, binary quadratic forms, and more.

Trick: Adding Numbers Quickly by Rounding Off

Suppose you want to add: 397 + 586

Normal Method:

You’d add digit by digit → takes more time.

Smart Trick:
1. Round one number to the nearest 100:
• 397 → 400 (add +3).
2. Add quickly:
• 400 + 586 = 986.
3. Subtract the extra (since you added +3):
• 986 – 3 = 983 ✅

⸻

⚡ Why It Works?

You’re just making the numbers easier to add (mental maths), then adjusting back.

Coolest math facts

Did You Know….
There is no Roman numeral for zero.
If 23 people are in the same room, there is a 50% chance that two people will have the same birthday.
1000 is the only number from 0 to 1000 that has an “a” in it.
Take any shape with the same perimeter, and a circle still possesses the largest area.