A mathematical problem has become extremely popular on the Web, which was posted on his Facebook page by Singaporean TV presenter Kenneth Kong. Internet users were excited by the complexity of the task, as well as the remark that it was designed for fifth-graders.
Mashable drew attention to the new Internet virus.
In four days, over 5,000 Facebook users have shared Kong's post. Internet users were excited by the complexity of the task, as well as the comment of the TV presenter that it was designed for fifth graders.
The condition of the problem looks as follows.
“Albert and Bernard just met Cheryl and wanted to know when her birthday. Cheryl gave them a list of ten possible dates:
- May 15, May 16, May 19;
- June 17, June 18;
- July 14, July 16;
- August 14, August 15, August 17.
Then Cheryl told Albert what month she was born, and Bernard - what date. After that, the following conversation took place between the men.
“I don’t know when Cheryl’s birthday, but I know that Bernard doesn’t know either,” Albert said.
“At first I didn’t know when Cheryl’s birthday, but now I do,” Bernard replied.
“And now I know when Cheryl was born,” Albert said.
So when is Cheryl's birthday?"
The entry on Kenneth Kong's page has collected more than 1,500 comments and has been widely disseminated in other blogs, as well as in the media. Many participants in the discussion admitted that they felt too stupid because they could not solve a problem for fifth grade students.
However, as it turned out two days later, the problem turned out to be not an ordinary school problem, but an Olympiad problem. In addition, it was designed for 14-year-old students. This was reported to Kong by representatives of the organization SASMO (Singapore and Asean Schools Math Olympiads). The TV presenter himself admitted that he even quarreled with his wife on the basis of discussing this problem.
Later, a solution to the problem appeared in the Study Room community.
“First we have to find out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows Cheryl's date of birth. Thus, Albert knows the month.
From the first line, we know that Albert is confident that Bernard does not know the date of birth. Therefore, May and June can be excluded, since the 19th number is present only in May (among the dates indicated in the list), and the 18th number is only in June.
Thus, Bernard knows that May and June can be excluded.
After that, Bernard can find out the month when Cheryl was born. The dates remain July 16, as well as August 15 and August 17. At the same time, July 14 and August 14 can be excluded, since if Cheryl had told Bernard that her birthday was on the 14th, then Albert would not have been able to give an exact answer about the full date.
Subsequently, Albert said that he, like Bernard, knows Cheryl's date of birth, then he knows that she was born in July. If it was August (recall that Albert had data about the month), then he could not say for sure whether his birthday falls on August 15 or 17.
Thus, Cheryl was born on July 16th."
