[math-fun] Singapore exam question
The whole internet apparently knows about this problem, so math-fun might as well too... http://cdn.theatlantic.com/assets/media/img/posts/2015/04/11155125_385751114...
[I'm getting July 16. Thus qualifying me to be a Singaporean 5th grader, or whatever it was.] -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
On 15/04/2015 22:49, meekerdb wrote:
I get June 17. If Bernard were given 16 as the date he'd be uncertain between May and July and Albert couldn't resolve them.
No, I agree with Warren that July 16 is correct. B is given 16 and is uncertain between May and July, as you say; that is why at first he doesn't know when C's birthday is. But once he's told that A knows B doesn't know C's birthday, he can eliminate May (because if A were told May, A wouldn't know that B doesn't know because for all A knows the date could be May 19 and then B *would* know). That's why at step 2 B says he knows now. (And then at step 3 A knows, because that sort of reasoning wouldn't work if B had been told 14 instead of 16.) -- g
No, July 16 is correct. Bernard knows that the month has to be July or August, based on Albert saying that Bernard can't know (which rules out the 18th and 19th, which occur in May and June). Since Bernard then says he knows, the day can't be the 14th, and when Albert says he knows, that rules out August, leaving only July 16. June 17 doesn't work since Albert has already ruled out June with his first response. If the month were June, then Albert wouldn't initially know that it wasn't June 18, so he would not know that Bernard didn't know the answer from the start. Tom meekerdb writes:
On 4/15/2015 12:13 PM, Warren D Smith wrote:
[I'm getting July 16. Thus qualifying me to be a Singaporean 5th grader, or whatever it was.]
I get June 17. If Bernard were given 16 as the date he'd be uncertain between May and July and Albert couldn't resolve them.
Brent
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
participants (4)
-
Gareth McCaughan -
meekerdb -
Tom Karzes -
Warren D Smith