
Notices 
Welcome to the International Skeptics Forum, where we discuss skepticism, critical thinking, the paranormal and science in a friendly but lively way. You are currently viewing the forum as a guest, which means you are missing out on discussing matters that are of interest to you. Please consider registering so you can gain full use of the forum features and interact with other Members. Registration is simple, fast and free! Click here to register today. 
1st December 2017, 11:47 PM  #1 
Graduate Poster
Join Date: Sep 2011
Posts: 1,726

Math experts: What is the value of this expression?
This is from a mathematics qualification pretest from an online physics course. I'm not sure I agree with the official answer. I'm curious what you all think?
What is the value of the following expression? 
1st December 2017, 11:56 PM  #2 
Graduate Poster
Join Date: Apr 2011
Posts: 1,279


2nd December 2017, 12:01 AM  #3 
Critical Thinker
Join Date: Dec 2008
Posts: 366

Python agrees:
Code:
>>> total = 0 >>> for j in (1,2): ... for k in (2,3): ... for l in (3,4): ... total += j + k + l ... >>> total 60 
2nd December 2017, 12:07 AM  #4 
Penultimate Amazing
Join Date: Apr 2009
Location: Iowa USA
Posts: 12,131

So you're saying that Jabba is numerically immortal?

__________________
"Sufficiently advanced malice is indistinguishable from incompetence. = godless Dave 

2nd December 2017, 12:23 AM  #5 
Penultimate Amazing
Join Date: May 2006
Posts: 15,384


__________________
My new blog: Recent Reads. 1960s Comic Book Nostalgia Visit the Screw Loose Change blog. 

2nd December 2017, 12:25 AM  #6 
Critical Thinker
Join Date: Dec 2008
Posts: 366

Shortest answer?
Averages of each range (12, 23, 34) are 1.5, 2.5, 3.5. Sum of those is 7.5. Eight combinations summed and 8 x 7.5 = 60. 
2nd December 2017, 12:14 PM  #7 
Philosopher
Join Date: Jun 2010
Posts: 6,098

There's three sigma symbols in the equation, and twenty symbols total. 3*20 = 60.

2nd December 2017, 04:42 PM  #8 
Critical Thinker
Join Date: Dec 2008
Posts: 366

Funny, but let's say we change the ranges for each sigma so that instead of 12, 23, and 34 we're summing over (say) 15, 37, and 59.
Averages for the three new ranges are 3, 5, 7 which sum to 15. And there are 5 x 5 x 5 = 125 combinations. 125 x 15 = 1875. Using averages like this works because fundamentally everything we'e doing is addition and addition is also commutative, and finally the sigma operation is spanning a uniform range of values... But there are still 20 symbols. Hmm.... waiting for your new "answer"! ;) 
2nd December 2017, 04:50 PM  #9 
Philosopher
Join Date: May 2007
Posts: 7,402

May I ask a historical question?
The symbols in that mathematical equation when would they have come into existence? Or put another way how far back in time could you go and still have an educated man understand that equation? I'm asking because I am thinking of stealing that for a book but it is set in 1839 and would that be possible to write at that time? Thanks 
2nd December 2017, 05:35 PM  #10 
Critical Thinker
Join Date: Dec 2008
Posts: 366

According to wikipedia (https://en.wikipedia.org/wiki/Histor...tical_notation) Euler used capital sigma for summation, and Euler lived in the 18th century so it seems you would be in good company to be using that notation in 1839. Euler was born in 1707 and died in 1783.

3rd December 2017, 12:40 AM  #11 
Philosopher
Join Date: May 2007
Posts: 7,402


3rd December 2017, 12:51 AM  #12 
Skeptical about skeptics
Join Date: Sep 2010
Location: 31°57'S 115°57'E
Posts: 12,813


__________________
"The process by which banks create money is so simple that the mind is repelled. Where something so important is involved, a deeper mystery seems only decent."  Galbraith, 1975 

3rd December 2017, 06:29 AM  #13 
Hyperthetical
Join Date: Nov 2006
Location: Pennsylvania
Posts: 13,750


__________________
A zømbie once bit my sister... 

Bookmarks 
Thread Tools  

