BEATCALC:  Beat the Calculator!

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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 sequence of consecutive odd numbers

  1. Choose a 2-digit odd number. Add all the odd numbers starting with one through this 2-digit number:
  2. Add one to the 2-digit number.
  3. Divide this sum by 2 (take half of it).
  4. Square this number. This is the sum of all odd numbers from 1 through the 2-digit number chosen.

   Example:

  1. If the 2-digit odd number selected is 35:
  2. 35+1 = 36 (add 1).
  3. 36/2 = 18 (divide by 2) or 1/2 × 36 = 18 (multiply by 1/2).
  4. 18 × 18 = 324 (square 18): 18 × 18 = (20 - 2)(18) = (20 × 18) - (2 × 18) = 360 - 36 = 360 - 30 - 6 = 324.
  5. So the sum of all the odd numbers from one through 35 is 324.

   See the pattern?

  1. If the 2-digit odd number selected is 79:
  2. 79+1 = 80 (add 1).
  3. 80/2 = 40 (divide by 2) or 1/2 × 80 = 40 (multiply by 1/2).
  4. 40 × 40 = 1600 (square 40).
  5. So the sum of all the odd numbers from one through 79 is 1600.
     


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12 February 1996
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