BEATCALC:  Beat the Calculator!

___________________________________________
Back to Calculation Tips & Tricks
___________________________________________

From the BEATCALC mailing list:
a weekly service from B. Lee Clay, archived here by the Math Forum.
To subscribe to the BEATCALC mailing list, write to BEATCALC@aol.com.


 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


   Add sequences of numbers in the 10's

  1. Choose a 2-digit number in the 10's. To add all the 10's from 10 up through this number and down from it:
  2. Square the 2nd digit of the number
    (keep the carry)   _ _ X
  3. The number of terms is 2 × the 2nd digit + 1.
  4. The first digits = the number of terms
    (+ carry). nbsp; X X _

   Example:

  1. If the 2-digit number in the 10's selected is 16:
    (10 + 11 + 12 ... 16 + 15 + 14 ... 10)
  2. Square the 2nd digit of the number:
    6 × 6 = 36 (keep carry 3)   _ _ 6
  3. No. of terms = 2 × 2nd digit + 1:
    2 × 6 + 1 = 13
  4. No. of terms (+ carry): 13 + 3 = 16   1 6 _
  5. So the sum of the sequence is 166.

   See the pattern?

  1. If the 2-digit number in the 10's selected is 18:
    (10 + 11 + 12 + ... 18 + 17 + 16 + 15 ... 10)
  2. Square the 2nd digit of the number:
    8 × 8 = 64 (keep carry 6)   _ _ 4
  3. No. of terms = 2 × 2nd digit + 1:
    2 × 8 + 1 = 17
  4. No. of terms (+ carry): 17 + 6 = 23   2 3 _
  5. So the sum of the sequence is 234.
     


[Privacy Policy] [Terms of Use]

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

© 1994-2008 Drexel University. All rights reserved.
http://mathforum.org/
 The Math Forum is a research and educational enterprise of the Drexel School of Education.The Math Forum is a research and educational enterprise of the Drexel School of Education.

8 February 1999
Web page design by Sarah Seastone