Some friends and I were talking about the recent Dayton police lawsuit – where people are suing the city because only a small percentage of African American applicants pass the entrance exam. In order to squash concerns that the exam was somehow racist, the city released a bunch of sample questions from the exam. After reading it, I can confirm that it’s not really racist. It’s probably another case of correlation vs causation at work here. If less blacks take the test than whites, less blacks are going to pass the test.
Looking at the test though, some friends of mine and I kept staring at question #9. Question 9 reads:
A parade has been scheduled to run 5 miles through the city. It is desirable to have an officer stationed every 3 blocks. If there are 12 blocks in a mile, how many officers will be needed?
A) 13
B) 15
C) 18
D) 20
It’s easy to see the logic that they want you to do here. 12 blocks X 5 miles = 60 blocks. Divide that by 3 and you get 20.
20 seems like the right answer, until you actually think about how you’d implement this in the real world. In the real world you’d want to put an officer at the start and finish of the race, so you’d need 21 officers to work it, not 20. The logic that the question uses is not the logic you’d use if you were really trying to position police officers along a parade route.
It’s a classic example of what we computer scientists call the “fencepost” or “off by 1” problem.
The problem here is that you don’t want to count the number of 3 block sections, you want to count the number of officers that have 3 block sections between them.
It’s the difference between counting sections of fence or fence posts. Let’s look at a graphical example.
Assume this is a fence:
|—|—|—|—|
This fence has 4 sections, but needs 5 posts to connect them. So, if I want a 4 mile fence with 1 mile long sections, I’ll need 5 fence posts.
The same holds true with positioning police officers at a marathon.
The error most often occurs when counting starts at 1 rather than 0 – and it’s why we computer scientists always write things like:
for (i=0; i<5; i++)
instead of
for (i=1; i<6; i++) or, the similarily confusing for (i=1; i<=5; i++)
March 19th, 2009
I’m starting to notice an ugly trend among online newspapers. Unlike most blogs and online only sources, traditional newspapers don’t link to websites in articles – even when the website is the focus of the article.
I must have read about 4 or 5 articles earlier about wikileaks leaking the ACMA list of banned websites – but none of the articles included a link to said list. A quick Google search showed that no major newspaper linked to the list, yet every major blog that covered the story did. I can’t help but wonder if there is some sort of editorial policy at work here, or if the newspapers are just afraid of linking to “improper” content. (which, in this case was simply a list of more links to the actual websites – many of which feature porn.)
Somebody on Twitter pointed out that they could be doing so out of legal concerns – but I’m fairly sure that it’s not illegal to link to something in America. Linking is no different than giving directions – even a first year law student knows that if I tell you how to make a bomb and where to get the parts, that doesn’t make me liable for what you do with the bomb.
Ordinarily I’d be convinced that fear of legal repercussions was the motive, but I’ve seen this phenomenon many other times too.
Just yesterday I read a Times piece about a NFL mock draft that included several predictions, but not a link to the actual draft that the article was about. Instead, they just listed the name of the sportswriter who wrote the mock draft and forced me to find it on Google.
Almost every day I receive a Google alert about a news news source that mentioned my website, NoSlang.com in one of their stories – and the result is always the same: A full article about internet slang, quotes and top 10 lists pulled directly from the site, but only a text mention instead of a hyperlink. That’s fine if the story were appearing in print, but it’s as if all they did was copy and paste to put the story up on the web.
Actually, that copy and paste theory makes a lot of sense when I think of the broader picture of most newspapers. It seems to me that newspapers are still so out of touch with the internet that they don’t realize how important it is to readers to add hyperlinks to the online versions of their stories. Can that be true? If so, it’s no wonder that a lot of newspapers are failing.
March 19th, 2009
