Time for a puzzle

[Charlie Reams]

Chas and Dave are twins in their twenties. Chas, the younger of the two, says to Boris that, if he were to tell him the first letter of the month in which he was born, Boris could not know which month it was, but if he were to tell him also the next letter, he would know. Dave says to Alex, out of earshot, that if he were to tell him the last letter of the month in which he was born, Alex could not know which month it was, but if he were to then tell him the penultimate one also, he would know. The brothers were born at a weekend. What year was it?

[Stolen from The Sunday Times]

[Paul Howe]

Hmm, I'm not sure if I've quite cracked this but I've got two answers:

April and August are the only months satisfying the first condition but neither satisfy the second, so they must be born in consecutive days on different months. May satisfies the second condition but not September, and since they're born at a weekend we're looking for a year on which April 30th falls on a Saturday and 1st May a Sunday. Since Stewart Gordon is not available, I browsed previous years calendars using my computer clock and found two such years, 1983 and 1988, which allow the twins to be in their twenties.

So in conclusion, I can't see what I've done wrong but I've obviously missed something.

[Jon Corby]

Dave says to Alex, out of earshot

So Alex can't hear him?

[Paul Howe]

Dave says to Alex, out of earshot

So Alex can't hear him?

Ha, I thought that too. The thing that's bothering me is I can't work out what difference it makes that the information is told to two different people.

[Charlie Reams]

So in conclusion, I can't see what I've done wrong but I've obviously missed something.

You made a slight over-optimisation.

Edit: On second thoughts, maybe you didn't. *Scratches head*

Edit #2: This puzzle was published a few weeks ago, but it occurs to me that the ambiguity disappears if the puzzle was intended to be published before May.

[Jon Corby]

I get the same answer as you Paul. Maybe we were supposed to be told that Chas and Dave were originally part of triplets, but the third one was trampled to death during the Brixton riots caused by the shooting of Dorothy Groce, thus telling us that they must have been born before 1985.

[Charlie Reams]

The thing that's bothering me is I can't work out what difference it makes that the information is told to two different people.

I think that's to avoid Alex using the information from Chas as part of his reasoning, because that would allow him to conclude which month it was knowing only the last letter.

[Paul Howe]

The thing that's bothering me is I can't work out what difference it makes that the information is told to two different people.

I think that's to avoid Alex using the information from Chas as part of his reasoning, because that would allow him to conclude which month it was knowing only the last letter.

Ah, makes sense.

I may post the one about the villagers who don't know their eye colour sometime, it seems to have been popular on the internet recently though so maybe people have already seen it.

[Gary Male]

You've got the twins the wrong way round, surely? Chas is the younger, so he can be born in August. Dave is older, he can be born in July. 1982 works for me.

[Paul Howe]

You've got the twins the wrong way round, surely? Chas is the younger, so he can be born in August. Dave is older, he can be born in July. 1982 works for me.

D'oh! Bit of a cockup there, and perhaps a good example of a mental bias in assuming the first twin is older, despite the clear statement that he's younger.

[Jason Larsen]

September 1985.

That's just a shot in the dark!

[Howard Somerset]

Chas and Dave are twins in their twenties. Chas, the younger of the two, says to Boris that, if he were to tell him the first letter of the month in which he was born, Boris could not know which month it was, but if he were to tell him also the next letter, he would know. Dave says to Alex, out of earshot, that if he were to tell him the last letter of the month in which he was born, Alex could not know which month it was, but if he were to then tell him the penultimate one also, he would know. The brothers were born at a weekend. What year was it?

[Stolen from The Sunday Times]

Before I'd got to the end of that post, Charlie, I thought to myself, I've seen that somewhere else, very recently. And then I read to the end and remembered where I'd seen it. It was a good one, and yet another that I've submitted, probably in vain. Must revert to the Observer, where I've won three of them.

[Gary Male]

I may post the one about the villagers who don't know their eye colour sometime, it seems to have been popular on the internet recently though so maybe people have already seen it.

Please do. I love the puzzles based on eye colour, hat colour, and so on.

[Joseph Bolas]

I may post the one about the villagers who don't know their eye colour sometime, it seems to have been popular on the internet recently though so maybe people have already seen it.

Please do. I love the puzzles based on eye colour, hat colour, and so on.

You should definitely post it. If people know it, they can keep quiet and the people who don't know it can have a go at solving it .

[Gavin Chipper]

You've got the twins the wrong way round, surely? Chas is the younger, so he can be born in August. Dave is older, he can be born in July. 1982 works for me.

I've just had a look at this, and I came up with the same answer as you.