Tuesday, 14 April 2015

This Math Question Is Going Viral, No One Could Solve It Easily. Want To Try?

Kenneth Kong, presenter of a TV show ‘Hello Singapore’ has made a math question that goes viral all over the Internet.
A stream of comments and shares can be seen after the question was posted. The question has a very simple solution to it but appears to be tricky initially. Kong clarified that the question is actually set for a 14 years old student in Singapore and Asean Schools Math Olympiad.
Want to solve the problem? Give it a try.
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15 May 16 May 19
June 17 June 18
July 14 July 16
August 14 August 15 August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.
Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.
Albert: Then I also know when Cheryl’s birthday is.
So, when is Cheryl’s birthday?
The solution involves using logic to deduce the dates which can’t possibly be Cheryl’s birthday.
The dates range from 14 to 19 among the 10 that are given with only 18 and 19 occurring once. Albert was told the month rather than the day, first says he doesn’t know when her birthday is – disqualifying both 18 and 19 as possible days.If Cheryl had told Albert that the month was May or June, then the day could have been May 19 or June 18, and Bernardmay have known the right day. But the question says, Albert knows Bernard does not, meaning that Cheryl has said her birthday is in either July or August.
Out of the five remaining days in July and August, the day ranges from 14 to 17, with 14 appearing twice.
If Cheryl told Bernard her birthday was on the 14th, then he would not have known but, he does, meaning it can’t be on the 14th.
That leaves only 3 possible days: July 16, August 15, and August 17.
After Bernard speaks, saying he knows the birthday, it eliminates August from the list since he still wouldn’t have known whether it was August 15 or 17.
Hence it can be concluded that Cheryl’s birthday is on July 16.
Do you think it was an easy sum to do? Could you solve it initially? If not, must try this way. Check its difficulty level and tell us whether it’s really worth for a kid of 14?