Scribd
Upload
71 views2 pages

Calculation Tricks

The document provides various calculation tricks to enhance speed and accuracy in math, including methods for multiplying by 5, 11, and 9, as well as squaring numbers ending in 5. It also covers quick percentage calculations, multiplication of two-digit numbers close to 100, and divisibility rules. Regular practice of these techniques is encouraged for improved mathematical skills.

Uploaded by

jaycharole.work
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
71 views2 pages

Calculation Tricks

The document provides various calculation tricks to enhance speed and accuracy in math, including methods for multiplying by 5, 11, and 9, as well as squaring numbers ending in 5. It also covers quick percentage calculations, multiplication of two-digit numbers close to 100, and divisibility rules. Regular practice of these techniques is encouraged for improved mathematical skills.

Uploaded by

jaycharole.work
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 2

Calculation Tricks for Fast Math

1. Multiplying by 5

• If the number is even: Half the number and add a zero.


• Example: 64 × 5 → 64/2 = 32 → 320
• If the number is odd: Subtract 1, halve it, then add 5.
• Example: 47 × 5 → (47 - 1) = 46 → 46/2 = 23 → 235

2. Multiplying by 11

• For a 2-digit number:


• Example: 23 × 11 → 2 (2+3) 3 → 253
• If sum exceeds 9, carry over: 78 × 11 → 7 (7+8=15) 8 → 7 + 1 = 8, 5 in middle → 858

3. Squaring Numbers Ending in 5

• Formula: (x5)^2 = x(x+1) and add 25 at the end.


• Example: 65² → 6×7 = 42 → 4225

4. Quick Percentage Calculation

• 10% → Move decimal one place left


• 5% → 10% ÷ 2
• 15% → 10% + 5%
• 25% → Divide by 4
• 50% → Half the number

5. Multiplying 2-Digit Numbers (Close to Base 100)

• Formula: (100 + a)(100 + b) = 10000 + 100(a + b) + ab


• Example: 103 × 104 = 10000 + 100(7) + 12 = 10712

6. Subtraction from a Base (like 1000, 10000)

• Subtract each digit from 9 and last digit from 10


• Example: 1000 - 487 = 512 → (9-4)(9-8)(10-7) = 512

1
7. Multiplying Numbers Near 100

• Example: 98 × 97 → Base = 100, Differences = -2 and -3


• Step 1: 98 – 3 = 95
• Step 2: -2 × -3 = 6
• Final: 9506

8. Divisibility Rules

• 2 → Last digit even


• 3 → Sum of digits divisible by 3
• 4 → Last two digits divisible by 4
• 5 → Last digit 0 or 5
• 6 → Divisible by 2 and 3
• 9 → Sum of digits divisible by 9

9. Square of Numbers Ending in 1, 9, etc.

• (x + 1)² = x² + 2x + 1
• (x - 1)² = x² - 2x + 1

10. Multiplying by 9

• 9 × a = (10 × a) - a
• Example: 9 × 26 = 260 - 26 = 234

Practice these regularly to boost your speed and accuracy!

You might also like