How can you easily add the numbers from 1 to 100?

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Discussion Overview

The discussion revolves around finding an easy method to sum the integers from 1 to 100. Participants explore various mathematical approaches, visualizations, and formulas related to arithmetic progressions and series.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants suggest using the formula for the sum of an arithmetic series, specifically stating that the sum can be calculated as (n(n + 1))/2, where n is the last number in the series.
  • One participant proposes a visualization technique by arranging the numbers in pairs that sum to a constant value (101) and calculating the total based on the number of pairs.
  • Another participant introduces the concept of visualizing the sum using square arrays and off-diagonal elements, leading to the same result of 5050.
  • Some participants express curiosity about extending the summation to non-integer values, such as summing 1 + 1/n for n from 1 to 100, noting the complexity of the harmonic series involved.
  • There are mentions of historical anecdotes, such as Gauss's method of summing integers, which adds a narrative element to the discussion.
  • A few participants provide alternative methods and formulas, including visual representations and rearrangements of the summation process.

Areas of Agreement / Disagreement

While many participants agree on the basic formula for summing integers, there are differing methods and visualizations presented, indicating that multiple approaches are valid. The discussion remains open-ended regarding the extension of these methods to non-integer sums.

Contextual Notes

Some participants note that while they provide various methods, the original poster requested a simple solution, suggesting that the complexity of some explanations may not align with that request.

Who May Find This Useful

This discussion may be useful for those interested in mathematical reasoning, particularly in the context of arithmetic series and their applications, as well as for individuals exploring different methods of summation.

  • #31
Air said:
1+100=101, 2+99=101, 3+98=101 etc. There are 50 pairs of these so it is 101 times 50 which equals 5050.

Finally someone who didn't make the problem more complicated than was necessary and explained it the same exact way that Euler did it (or was it Gauss?).
 
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  • #32
i have somee good, yet simple brain teaasers, if any of you could give me advice on how to post them, that's be great, but for now, i'll just write a cool one here:a homeless man can collect 5 cigar butts to make 1 cigar. he finds 25 cigar butts, how many cigars can he make(hint:he smokes them all as soon aas he makes them>(my o don't work>





make some kinda reply and ill getcha the answer
 
  • #33
Six?

To post a new teaser, go up one level to the https://www.physicsforums.com/forumdisplay.php?f=33 and click the "New Topic" button near the top left corner of the page.
 
  • #34
The asymptotic behavior has an interesting geometric interpretation:
http://img201.imageshack.us/img201/5534/staircasesumsd2.png

Now here is a related brainteaser: what is the sum
1^2 + 2^2 + 3^2 + 4^2 + ... + n^2
in the limit as n is large?
 
Last edited by a moderator:
  • #35
Edit: I probably should have posted this with a spoiler alert:

\fbox{\color{white}n^3/3}... (LaTeX with white text... click to view source.)
Fill a portion of a cube with a stack of sequential squares... the analogue of your diagram. It generalizes to higher dimensions.
 
Last edited:

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