Book on Mental Math

Overview

• Suitable for those with mental math anxiety or fear of numbers
• Teaches how to calculate almost anything in seconds, faster than a calculator

Structure of the Book

• 11 chapters (Chapter Zero to Chapter Infinity)
• Two forewords: one by Bill Nye, another by the late James Randy
• Chapter Zero: Quick tricks (e.g., multiplying by 11, squaring numbers that end in five)

Instructor and Author

• Arthur Benjamin, a professor of mathematics
• Known for live shows and TED Talks

Mental Math Techniques

Multiplying a Two-Digit Number by 11

1. Add the two digits of the number together
   • Example: 5 + 4 = 9
2. Place the result between the two digits of the number
   • Example: 54 * 11 = 594
3. If the result is more than 9, add 1 to the first digit
   • Example: 68 * 11
     • 6 + 8 = 14 → Place 4 between 6 and 8 → 748 (since 14, add 1 to 6)

Squaring a Two-Digit Number Ending in Five

1. Take the first digit of the number
2. Multiply it by the next higher digit
   • Example: 55
     • 5 (first digit) * 6 (next digit) = 30 → Actually 50*60 = 3000
   • Add 25 to the result as the last step
     • 3000 + 25 = 3025
3. Works with any two-digit number ending in five
   • Example: 65
     • 6 (first digit) * 7 (next digit) = 42 → Actually 60*70 = 4200
     • Add 25 → 4200 + 25 = 4225

Practicing the Methods

• Example problems for practice: 53 * 11 and squaring 35

Recommendations

• Watch Arthur Benjamin's TED Talk
• Book is packed with learning hacks
• Promotes Brilliant.org for learning with interactive lessons

Brilliant.org

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