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Different Sums (Posted on 2004-07-22) Difficulty: 3 of 5
There are 40 ways to make sums of three distinct positive integers total 25. (1+2+22 is such a sum, but 1+12+12 and 1+2+3+19 are not.)

How many different ways can three distinct positive integers sum to 1000?

  Submitted by Brian Smith    
Rating: 3.2500 (4 votes)
Solution: (Hide)
The simplest method is to simply list out all the possible sums:

1+2+997 to 1+499+500
498 sums with 1

2+3+995 to 2+498+500
496 sums with 2

3+4+993 to 3+498+499
495 sums with 3

4+5+991 to 4+497+499
493 sums with 4

.
.
.

329+330+341 to 329+335+336
6 sums with 329

330+331+339 to 330+334+336
4 sums with 330

331+332+337, 331+333+336, 331+334+335
3 sums with 331

332+333+335
1 sum with 332

The sum of the subtotals is 1 + 3 + 4 + 6 + ... + 493 + 495 + 496 + 498 = 82834.

Oskar gives a formula for any integer N here.

Richard goes more in depth with an equivalent formula here.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re: With a little help from awkVee-Liem Veefessional2004-07-30 07:08:55
re(2): My solutionRichard2004-07-24 14:54:36
re: My solutionJohn2004-07-24 06:17:39
My solutionJohn2004-07-24 06:15:21
re(3): Curious second differencesRichard2004-07-23 21:00:08
SolutionAnalytical SolutionRichard2004-07-22 23:07:39
Solutionre(2): Curious second differencesOskar2004-07-22 13:04:49
blunt force with c - same ans as firstvectorboy2004-07-22 11:18:51
Some Thoughtsre: Curious second differencesFederico Kereki2004-07-22 11:14:31
Some ThoughtsCurious second differencesFederico Kereki2004-07-22 11:09:54
SolutionUgly method with excelJuggler2004-07-22 11:06:05
Some ThoughtsHuman ApproachNick Williams2004-07-22 11:02:15
re(3): With a little help from awkCharlie2004-07-22 10:46:56
Solutionre(2): With a little help from awkCharlie2004-07-22 10:45:04
re(2): With a little help from awkFederico Kereki2004-07-22 10:42:59
re: With a little help from awkSing4TheDay2004-07-22 10:25:15
SolutionWith a little help from awkFederico Kereki2004-07-22 10:00:34
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