{"id":25359,"date":"2015-04-24T15:28:44","date_gmt":"2015-04-24T20:28:44","guid":{"rendered":"http:\/\/blogs.ams.org\/mathgradblog\/?p=25359"},"modified":"2015-11-01T23:23:25","modified_gmt":"2015-11-02T04:23:25","slug":"cheryls-birthday","status":"publish","type":"post","link":"https:\/\/blogs.ams.org\/mathgradblog\/2015\/04\/24\/cheryls-birthday\/","title":{"rendered":"When is Cheryl’s Birthday?"},"content":{"rendered":"
\"\"<\/a>

Photo acquired from Wikimedia Commons, the free media repository<\/p><\/div>\n

Birthdays are a fun tradition that you get to celebrate with your friends and family once a year…that is, if you tell them when your birthday is.\u00a0 In a logic puzzle that has been making the rounds on the Internet, Cheryl tells her new friends Albert and Bernard her birthday in a very unusual manner.<\/p>\n

<\/p>\n

 <\/p>\n

The puzzle goes as follows:<\/p>\n

Albert and Bernard just become friends with Cheryl, and they want to know when her birthday is.\u00a0 Cheryl gives a list of 10 possible dates.<\/p>\n

May 15\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 May 16\u00a0\u00a0\u00a0\u00a0 \u00a0 \u00a0\u00a0 May 19
\nJune 17\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 June 18
\nJuly 14\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 July 16
\nAugust 14\u00a0\u00a0\u00a0\u00a0 August 15\u00a0\u00a0\u00a0\u00a0 August 17<\/p>\n

Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.<\/p>\n

Albert:\u00a0 I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.
\nBernard:\u00a0 At first I don’t know when Cheryl’s birthday is, but I know now.
\nAlbert:\u00a0 Then I also know when Cheryl’s birthday is.<\/p>\n

So when is Cheryl’s birthday?<\/p><\/blockquote>\n

This puzzle was part of the Singapore and Asian Schools Math Olympiads (Sasmo), aimed at students around 15 years old.\u00a0 At first, it was reported that this problem was given to 11 year old students, which prompted an outcry about the unreasonable difficulty of standardized tests.\u00a0 However, once it became clear that the question was aimed at older students, the focus reverted back to the interesting logic behind the problem.\u00a0 Henry Ong, Sasmo’s executive director, showed the purpose of the problem by explaining that<\/p>\n

[There is] a place for some kind of logical and analytical thinking in the workplace and in our daily lives.<\/p><\/blockquote>\n

A full video explanation of the problem solution can be found here:\u00a0 Cheryl’s Birthday: Singapore’s maths puzzle baffles world<\/a>.<\/p>\n

In case it wasn’t enough of a challenge to figure out when Cheryl’s birthday is, check out this Transfinite Epistemic Logic Puzzle<\/a> that she, Albert, and Bernard played as a party game!<\/p>\n

<\/div>","protected":false},"excerpt":{"rendered":"

Birthdays are a fun tradition that you get to celebrate with your friends and family once a year…that is, if you tell them when your birthday is.\u00a0 In a logic puzzle that has been making the rounds on the Internet, … Continue reading →<\/span><\/a><\/p>\n

<\/div>\n","protected":false},"author":68,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[14,15,17],"tags":[],"class_list":["post-25359","post","type-post","status-publish","format-standard","hentry","category-math-in-pop-culture","category-mathematics-in-society","category-news"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p3gbww-6B1","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/posts\/25359","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/users\/68"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/comments?post=25359"}],"version-history":[{"count":5,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/posts\/25359\/revisions"}],"predecessor-version":[{"id":25368,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/posts\/25359\/revisions\/25368"}],"wp:attachment":[{"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/media?parent=25359"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/categories?post=25359"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.ams.org\/mathgradblog\/wp-json\/wp\/v2\/tags?post=25359"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}