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 even numbers from two through
              a selected 2-digit even number

  1. Divide the even number by 2 (or multiply by 1/2).
  2. Multiply this result by the next number.

   Example:

  1. If the 2-digit even number selected is 24:
  2. Divide 24 by 2 (24/2 = 12) or multiply by 1/2 (1/2 × 24 = 12).
  3. The next number is 13; 12 × 13 = 156.
    Ways to multiply 13 by 12:
    • Square 12, then add 12: 12 × 12 = 144, 144 + 12 = 156.
    • Multiply left to right. 12 × 13 can be done in steps: 12 × (10+3) = (12 × 10) + (12 × 3) = 120 + 36 = 156.
  4. So the sum of all the even numbers from two through 24 is 156.

   See the pattern?

  1. If the 2-digit even number selected is 42:
  2. Divide 42 by 2 (42/2 = 21) or multiply by 1/2 (1/2 × 42 = 21).
  3. The next number is 22; 21 × 22 = 462.
    Ways to multiply 22 by 21:
    • Square 21, then add 21: 21 × 21 = 441, 441 + 21 = 462.
    • Multiply left to right. 21 × 22 can be done in steps: 21 × 22 = (21 × 20) + (21 x 2) = 420 + 42 = 462.
  4. So the sum of all the even numbers from two through 42 is 462.
     


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14 January 1996
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