BEATCALC:  Beat the Calculator!

___________________________________________
Back to Calculation Tips & Tricks
___________________________________________

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



  Subtracting the squares of two numbers

  1. Select a 2-digit number and then choose a number two larger or two smaller.
  2. Multiply the middle number by 4.

   Example:

  1. If the the first number selected is 31:
  2. Choose 29.
  3. Multiply the number between them by 4: 4 × 30 = 120
  4. So (31)(31) - (29)(29) = 120.

   See the pattern?

  1. If the the first number selected is 63:
  2. Choose 61.
  3. Multiply the number between them by 4: 4 × 62 = 248
  4. So 63^2 - 61^2 = 248.

   One more:

  1. If the the first number selected is 73:
  2. Choose 75.
  3. Multiply the number between them by 4: 4 × 74 = 296
  4. So (75x75) - (73x73) = 296.
     


[Privacy Policy] [Terms of Use]

_____________________________________
Home || The Math Library || Quick Reference || Search || Help 
_____________________________________

© 1994-2014 Drexel University. All rights reserved.
http://mathforum.org/
The Math Forum is a research and educational enterprise of the Drexel University School of Education.The Math Forum is a research and educational enterprise of the Drexel University School of Education.

16 September 1996
Web page design by Sarah Seastone