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 a series of quadruples

  1. Have a friend choose a single digit number. (No restrictions for experts.)
  2. Ask your friend to jot down a series of quadruples (where the next term is always four times the preceding one), and tell you only the last term.
  3. Ask your friend to add up all these terms.
  4. You will give the answer before he or she can finish: The sum of all the terms of this series will be four times the last term minus the first term, divided by 3.

   Example:

  1. If the number selected is 5:
  2. The series jotted down is: 5, 20, 80, 320, 1280.
  3. Four times the last term (1280) minus the first (5):
    4000 + 800 + 320 - 5 = 5120 - 5 = 5115
    Divide by 3: 5115/3 = 1705
  4. So the sum of the quadruples from 5 through 1280 is 1705.

   See the pattern? Here's one for the experts:

  1. The number selected is 32:
  2. The series jotted down is: 32, 128, 512, 2048.
  3. Four times the last term (2048) minus the first (32):
    8000 + 160 + 32 - 32 = 8,160
    Divide by 3: 8160/3 = 2720.
  4. So the sum of the quadruples from 32 through 2048 is 2720.

Practice multiplying from left to right and dividing by 3. With practice you will be an expert quad adder.


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3 June 1996
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