A TV presenter in Singapore recently brought up a math problem that has been driving the Internet crazy. At first, the problem seems impossible to solve. Rattle your brain or phone a friend before you look at the solution below the picture.
First we need to figure out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows the birthday, so it must be that Albert knows the month.
From the first statement, we know that Albert is sure that Bernard doesn’t know the birthday, so May and June should be ruled out (the day 19 only appears in May and the day 18 only appears in June). In other words, if Albert had May or June, then he cannot be sure that Bernard doesn’t know, since Bernard could have had 18 or 19.
Then, Bernard is able to know which month it is. So it must be either July 16, August 15 and August 17 (not 14th as then he can’t know).
The question was originally thought to posed to fifth graders but was later clarified to be for 14-year-olds competing in the Singapore and Asean Schools Math Olympiads (SASMO). It was the first ever recorded leak from the competition’s booklets and will be replaced by the time Cambodia runs the competition. Read more…