Jigsaw to 14-year-old, who can not decide the entire Internet
April 11 Singapore presenter Kenneth Kong posted in his Facebook logical puzzles for students. Two days of social network users have shared more than 4,400 times to her and arranged with serious debate in the comments. In the story drew the attention of Mashable.
The first recording of Kenneth reported that the task assigned to the level P5 - suitable for 10-year-olds, but it was so difficult, that he even quarreled with his wife on the search for a solution. At the time of publication of the picture he did not know the answer, because the problem showed him the niece of his friend.
The problem Albert and Bernard have just met with Cheryl. They want to know when her birthday. Cheryl offered them ten possible dates: May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15 and 17 August. Then Cheryl said Albert month of his birth, and Bernard - day. Then a dialogue.
Albert: I do not know when Cheryl's birthday, but I know that Bernard does not know.
Bernard: At first I did not know when Cheryl's birthday, but know now.
Albert: Now I also know when Cheryl's birthday.
When Cheryl's birthday?
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Two days later, when the job has gained viral popularity of the network, with Kenneth contacted by representatives of SASMO (Singapore and Asean Schools Math Olympiads - Mathematical Olympiad for Singapore and ASEAN) and sent him an answer, adding that it is in fact intended for children 14 years (Sec 3 level).
According to the SASMO, for their ten-year practice of the contest work had not fall into the network, because the children are prohibited from using cell phones during their execution. Nevertheless, they decided to clarify the situation to the parents of children level P5 does not sounded the alarm because of the fact that their child is not able to solve the puzzle has spread across the network.
The decision Dat only 10, and the days are in the range of 14 to 19. However, only 18 and 19 number there once. If Cheryl's birthday the 18th or the 19th, then Bernard would have immediately said last month.
But where Albert knows that Bernard does not know the answer? If Cheryl Albert said that she was born in May or June, so her birthday may be May 19 or June 18. In this scenario, Bernard can know when Cheryl's birthday. The fact that Albert knows that Bernard does not know the answer, say that May and June can be eliminated, and Cheryl was born either in July or in August.
Initially, Bernard did not know when Cheryl's birthday. How he found the answer after a replica Albert? Of the remaining five dates in July and August, ranging from 15 to 17, only 14 met twice. If Cheryl Bernard would say that the day of her 14th birthday, so after a suggestion of Albert Bernard still could not give a precise answer. The fact that he immediately understood everything, said that Cheryl was not born the 14th. There remain three possible dates: July 16, August 15 and 17 August.
After Bernard spoke, Albert learned when Cheryl's birthday. If she told him that she was born in August, Albert could not know the exact answer, because of the three remaining two dates fall in August. So Cheryl was born on July 16.
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via tjournal.ru/paper/14-years-old-math
