Cheryl’s Riddle of a Birthday

JULY 16 is Cheryl’s birthday, but how and why? The vexation at not knowing hit me not once, but twice.

In the first place, I didn’t understand the problem, the one starring Cheryl the coy protagonist who sends Albert and Bernard on a wild cerebral chase to divine her birthday. For some reason, the wording felt strangely awkward. Says Bernard to Albert, “At first I don’t know … but I know now.” Albert’s response: “Then I also know …” Alas, poor me, At first I don’t know, but now I also don’t know!

Second, I still didn’t get it even after parsing the lines to the solution, the one offered by the Singapore and Asian Schools Math Olympiad. They looked like simple steps of logic, deduction and elimination, but still the ten different dates Cheryl offered to both Albert and Bernard floated about like fierce, feisty flies one couldn’t quite swat at.

Always, whenever my intelligence is called to question, my self-confidence takes a beating. Then I ask, “Is it me?” or “Is it the language?” As of this morning though, just before I downed my glass of orange juice, I’m glad to report that it isn’t me, it’s the language. That’s because I was reading the story covered by Kenneth Chang from The New York Times, versus The Straits Times coverage that left me feeling bruised and not quite bright over the last two days.

For starters, Chang offers to reword the problem and bravely said what was quietly stewing in my heart, that “the wording of the problem is terrible”:

… so here is a clearer version, which makes some of the assumptions more obvious but which does not change any of the underlying logic of the problem:

His new narrative is a godsend, for now I feel as if there’s a real conversation going on among the three, and not some mind-reading taking place between the boys. But that’s not the highlight of Chang’s write-up. He had done so many other good things to make the problem and the solution so lucid:

  1. He titles his piece, How to Figure Out Cheryl’s Birthday, rather than giving it the insipid header The Solution. Somehow, the former holds out so much more promise for me, and it does, ultimately, because the line speaks with so much clarity and confidence.
  2. He explains at the outset that the puzzle has “built-in assumptions” such as the one that “everyone is truthful.” Later, he’d reinforce this by reminding us that “the possibility that Albert is lying or confused is off the table.”
  3. He sets out the list of 10 dates in table form: “it helps,” he’d go on to say. True enough, it is this very table that would help me see the light.
  4. He writes the phrase, “eliminating half of the possibilities,” a line packed with not just meaning but a strong visual, for now my eyes immediately strike off the top half of his table (the May and June rows), so that all I’m left with is the bottom half, the July and August rows with five remaining dates.
  5. He brings everything to a heightened conclusion with the sentence fragment, “The same logical process again:”. Notice that colon. It always does wonders, as it does right here.

Thank you, New York Times. Thank you, Kenneth Chang! At first I don’t know, but now I also know!

Author: viv

Singapore-based writer cooking and baking at home, and writing about her kitchen adventures

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