Puzzles riddles paradoxes

[.SF.]

I like them but the random thread might not be the right place.

Here's one - you want to use a grill pan to toast three slices of bread but it's only wide enough for two. If it takes 20 seconds to toast one side what's the quickest you can toast all three slices on both sides.

[HobbitFeet]

slice 1 and slice 2 - first side

slice 1 (turned over) and slice 3 - slice 3 first side, slice 1 ready

slice 2 and slice 3 - the 2nd side of both


so 1 minute

[.SF.]

Nice one

[.SF.]

Maths (probability) question:

A pencil has five sides, on one of the sides it's printed with the words 'HB PENCIL', the other sides have nothing printed on them. If you roll the pencil on a table what is the probability it will come to rest with the printed side uppermost?

[Lady Murasaki]

1 out of 5. Or 1/5.

[Cobs]

[LordRaven]

Here's a proper puzzle that will baffle the boffins the world over because nobody can explain it...

"art0hur0moh"

[Lady Murasaki]

Here's a proper puzzle that will baffle the boffins the world over because nobody can explain it...

"art0hur0moh"

Needs a proper sleep pattern. And no screen time. And stop listening to the very miserable Jordon Peterson.

[.SF.]

I don't think there's been an explanation for what's wrong with the reasoning behind this one.

You can't give a class a surprise test.

Teacher tells class she will give them a surprise test one day next week, they won't know which day they're getting it. Someone points out it can't be Friday because if it hasn't happened by then it won't be a surprise. That leaves Thursday as the last possible day. But if it hasn't happened by then it won't come as a surprise so that rules out Thursday. Same reasoning rules out Wednesday and Tuesday, leaving Monday as the only possible day, but if Monday's the only possible day then it won't be a surprise.

So she can't give them the surprise test.

[Text]

I don't think there's been an explanation for what's wrong with the reasoning behind this one.

You can't give a class a surprise test.

Teacher tells class she will give them a surprise test one day next week, they won't know which day they're getting it. Someone points out it can't be Friday because if it hasn't happened by then it won't be a surprise. That leaves Thursday as the last possible day. But if it hasn't happened by then it won't come as a surprise so that rules out Thursday. Same reasoning rules out Wednesday and Tuesday, leaving Monday as the only possible day, but if Monday's the only possible day then it won't be a surprise.


So she can't give them the surprise test.

I don't quite get this. Maybe it's a comprehension problem on my part.

Now, it's not a surprise that the class is going to have a test cos she's told them they will be having one.
HOWEVER the day she chooses to give it, will certainly be a surprise cos the pupils don't know the day it will happen[unless of course it's the very last day-friday, as you say].

[Text]

What about the pencil puzzle? Let's have some feedback on that one, SF.

Like others have said, it should be a simple 1 in 5 chance.
Theoretically the etchings might make a difference in the calculations, cos the 5 surfaces are not identical but it will be a vanishingly small difference ... i think.

[.SF.]

Surprise test: I could have worded it better, the surprise element = they won't know in advance which day they'll be getting it.

Pencil: probability = zero.

[drum]

Surprise test: I could have worded it better, the surprise element = they won't know in advance which day they'll be getting it.

Pencil: probability = zero.

The pencil.. I was thinking that the side with writing on would be heavier and if you rolled it it would stop heavy side down.. I haven't tried that though.

[Lady Murasaki]

Surprise test: I could have worded it better, the surprise element = they won't know in advance which day they'll be getting it.

Pencil: probability = zero.

Are you saying you can’t roll a pentagonal pencil or that the printed bit was at the end which you’re now telling us is a side?

[Raggamuffin]

I don't think there's been an explanation for what's wrong with the reasoning behind this one.

You can't give a class a surprise test.

Teacher tells class she will give them a surprise test one day next week, they won't know which day they're getting it. Someone points out it can't be Friday because if it hasn't happened by then it won't be a surprise. That leaves Thursday as the last possible day. But if it hasn't happened by then it won't come as a surprise so that rules out Thursday. Same reasoning rules out Wednesday and Tuesday, leaving Monday as the only possible day, but if Monday's the only possible day then it won't be a surprise.

So she can't give them the surprise test.

That's an old one - I heard it in the late '70s, except it was a surprise party.