BEATCALC:  Beat the Calculator!

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Back to Calculation Tips & Tricks
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From B. Lee Clay


 Squaring Numbers

 Multiplying Numbers

 Dividing Numbers

 Adding Numbers

  1. even numbers 2 through selected 2-digit evens
  2. digits of square of repeating ones
  3. consecutive odds
  4. consecutive between 2 numbers
  5. sequence from 1 to selected 2-digit number
  6. sequence from 1 to selected 1-digit number and back
  7. sequences in the 10's
  8. sequences in the 20's
  9. sequences in the 30's
  10. sequences in the 40's
  11. sequences in the 50's
  12. sequences in the 60's
  13. sequences in the 70's
  14. sequences in the 80's
  15. series of doubles
  16. series of quadruples
  17. series of 10 numbers

 Subtracting Numbers

  1. 1's repeating, divide by 9, subtract 21
  2. 8's repeating, divide by 9, subtract 10
  3. squares of two numbers
  4. reversing/adding/subtracting 3-digit numbers

 Percents

  1. finding 2.5 percent
  2. finding 5 percent
  3. finding 15 percent
  4. finding 20 percent
  5. finding 25 percent
  6. finding 33 1/3 percent
  7. finding 40 percent
  8. finding 45 percent
  9. finding 55 percent
  10. finding 60 percent
  11. finding 70 percent
  12. finding 75 percent

Calculation
Practice Exercises

Full List


   Adding consecutive numbers between two
              numbers

   Choose two 2-digit numbers less than 20
     (no limits for experts).
   Add all the numbers between them:
  1. Add the numbers;
  2. Subtract the numbers and add 1;
  3. Multiply half the sum by this difference + 1, OR
    Multiply the sum by half the difference + 1.

   Example:

  1. If the two numbers selected are 6 and 19:
  2. Add the numbers: 6 + 19 = 25.
  3. Subtract the numbers: 19 - 6 = 13. Add 1: 13 + 1 = 14.
  4. Multiply 25 by half of 14: 25 × 7 = 175.
  5. So the sum of the numbers from 6 through 19 is 175.

   See the pattern?

  1. If the two numbers selected are 4 and 18:
  2. Add the numbers: 4 + 18 = 22.
  3. Subtract the numbers: 18 - 4 = 14. Add 1: 14 + 1 = 15.
  4. Multiply half of 22 by 15: 11 × 15 = 165 (10 × 15 + 15).
  5. So the sum of the numbers from 4 through 18 is 165.

Practice with examples restricted to less than 20, then advance to larger numbers. You will impress your friends when you beat the calculator.


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4 November 1996
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