So, I’ve been following the ‘viral’ story of the Singapore Math Problem. Here’s the reprinted answer for those that haven’t seen it (from this site). That site also publishes an article about why it can’t be “August 17” (as stated on some other websites), either. The problem with all of this is that they are ALL WRONG!
The question below has Albert saying, “I don’t know when Cheryl’s birthday is”. This is fine. However, his next statement, “but I know that Bernard does not know too”, is the problem. Albert DOES NOT know that Bernard does not know. This is an assumption on Albert’s part, NOT a fact as suggested by the solution. Cheryl very well could have told Bernard that her birthday ‘date’ was the 18th or the 19th. Both of these satisfy the first part of Albert’s statement (that’s he doesn’t know, because he was perhaps given the month of May or June). In which case, Albert is incorrect in his assumption.
Now, if the question was changed to add, “Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively, without either of them having enough information on their own to be sure.” Then, we could use the logic in the answer and get to a solution.
If, however, you stick with the original question as stated in the test. Than, there just isn’t enough definitive information to get to the solution. I do appreciate the logic and agree with some that have suggested that maybe Albert and Bernard should just move on. If she can’t give us a simple answer to a friendly question, who wants to be friends with Cheryl, anyway?