Math olympiads boast some of the brightest judgement to enter high school . The problem given to competitors are meant to be crafty , but there ’s one question that ’s so notorious it even has its ownWikipedia page .
The " Cheryl ’s natal day " conundrum first appear on a math Olympics tryout given to students in Singapore . Local television presenter Kenneth Kong posted a picture of the original text on Facebook in 2015 . The ungainly English makes for a riddle that ’s tough to decipher , soThe New York Timespublished an edited version that reads as postdate :
If you take through this promptly , it ’s easy to get lost . How is it possible to guess someone ’s birthday when you only have one one-half of the date ? And how could Albert and Bernard help each other guess correctly without divvy up their intel out loud ? Thesecret liesin the possible date Cheryl chooses to share .
In her list , every sidereal day is repeated once except for the 18th and the nineteenth — so if she had whispered “ 18 ” in Bernard ’s ear he would immediately know her birthday was June 18 , and if she ’d whispered “ 19 ” he ’d know it was May 19 . Bernard confirms it could n’t be either of those date when he say he “ did n’t be intimate originally . ” That have in mind June and May are no longer options for Albert , which constrict it down to five opening : July 14 , July 16 , August 14 , August 15 , and August 17 .
When Bernard say “ I did n’t know[ … ]but now I do ” that disqualify 14 , because in that case he would have two potential solution ( July 14 and August 14 ) to choose from . These allow for three date — July 16 , August 15 , and August 17 — that could be right . When Albert says , “ Well , now I know too ! ” he pass July from the par because that ’s also a case where he ’d be leave with two option . July 16 is therefore the one true answer .
Does your principal hurt yet ? Unfortunately , maths job intended for grade - schoolers in Singapore do n’t get much simpler . Check out this perplexinghomework problemgiven to first - grader if you necessitate convincing .
[ h / tThe New York Times ]
