Here is the “Cheryl Question” from Singapore that, according to Terrance Ross of the Atlantic, provoked “hysteria” around the web:
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15 May 16 May 19
June 17 June 18
July 14 July 16
August 14 August 15 August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know either.
Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.
Albert: Then I also know when Cheryl’s birthday is.
So when is Cheryl’s birthday?
Can you solve it? Well, I can’t. So that means that I’m dumber than a Singapore fifth-grader!
Except that it doesn’t. First of all, as Terrance points out, some of the “hysteria” was based on the notion that this was given on a fifth-grade school exam. But in fact it was intended for higher grades. He concludes “And even though the “Cheryl’s Birthday” question may be atypical of the average Singaporean classroom, perhaps it’s still worth asking: Are you smarter than a (Singaporean) 10th-grader?”
Except that even that doesn’t go far enough. Terrance links to a site in Singapore that gives us the real scoop, which he apparently did not bother to read in detail. This question was given in the Singapore Math Olympiad, not in a typical or atypical classroom. Furthermore, there’s no indication that any student who took the Olympiad got it right. So why the hysteria, which even affected Terrance?
Because human beings (not just Americans) have an instinctive tendency to confuse an outlier with the mean. The mean, after all, is boring. It’s always there. Outliers are exciting. The mean puts us to sleep, but outliers wake us up (literally; we’re hard-wired that way). A, um, mean understanding of sampling and statistics might cure us of misapplying an instinct that Mother Nature has instilled in us over the past several billion years. But apparently we aren’t there yet.
Alex Bellos explains how to solve the problem here
