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+--- Thread: Math puzzles (/thread-4500.html)
Math puzzles - jxu - 08-22-2014
Start off easy.
#1
Find the number of ordered triples (a, b, c) where a, b, and c are positive integers, a is a factor of b, a is a factor of c, and a + b + c = 100
RE: Math puzzles - AFtExploision - 08-22-2014
(5, 20, 75)
RE: Math puzzles - tyler569 - 08-22-2014
200.
102 if you don't count 1 as a factor.
I wrote some code to calculate this for arbitrary sums which I will post when I am not on my phone.
Fun fact: if b must also be a factor of c, that number drops to 20.
http://pastie.org/9495201
(Briefly) tested working on python2.7 and 3.4
RE: Math puzzles - jxu - 08-23-2014
You are not allowed to use a calculator or program a solution.
#2 (more easy)
Solve for a17 when a1 + a2 + a3 = 1, a2 + a3 + a4 = 2, ... a16 + a17 + a1 = 16, a17 + a1 + a2 = 17
RE: Math puzzles - Iceglade - 08-23-2014
Here's a really easy (but still interesting) one:
Is 362887 prime or composite? Don't try to factor it, look for a trick (and try to generalize!)
RE: Math puzzles - jxu - 08-23-2014
I dunno, it was faster to do trial division
RE: Math puzzles - Iceglade - 08-23-2014
(08-23-2014, 01:43 AM)͝ ͟ ͜ Wrote: I dunno, it was faster to do trial division
Well that's damn boring.
hint: what is 362880
RE: Math puzzles - jxu - 08-23-2014
Oh it's 9!
I don't know if you expected anyone to know that off the top of their head