Brain teaser thread

[Immortal Wombat]

His horse was called Monday, then he bought a new horse named Friday.

[CyberGnu]

Eh, why would he walk on his first horse?

But in essence correct

Your turn.

[Immortal Wombat]

oh, yeah. Different version caught me.

This is easy, but anyway:

Three busloads of students drove off on a field trip.
Fifty students rode the first bus. The ratio of boys to girls on this bus was 2:3.
The ratio of boys on the first bus to boys on the second bus was 5:6, though the ratio of girls to boys on bus 2 was 50:50.
The ratio of girls on the 3rd bus to girls on the 2nd bus was 7:8.
Boys comprised 40% of the students on the third bus.

[Dauphin]

And the question is.....where were they going?

A: On a field trip.

[Urban Ranger]

Yeah, so what's the question?

[Immortal Wombat]

how many boys and girls are there?

[Paul Hanson]

I make it to be 58 boys and 75 girls in total.

[Immortal Wombat]

yes. it is.

[Urban Ranger]

Okay, here is a simple one.

There is a jar with an amoeba inside. It splits every minute. In an hour the jar will be filled.

Suppose that there are two amoebae to start with, how long will it take to fill the jar?

[Urban Ranger]

This is interesting.

Check out this magic trick and see if you can figure out how it works.

[JohnM2433]

If there are two amoebae to start with, it will take 59 minutes to fill the jar, as the situation at the start is the same as it was after one minute in the first instance (59 minutes remaining).

It was fairly obvious to me how that "trick" works. I checked just to make sure. With some sleight of hand, you could probably do the same thing with real cards.

[JohnM2433]

OK, this same basic problem, only in another form, was covered in another thread. But I can't think of anything better, so...

You are on a game show, and you are shown three doors. The grand prize is behind one of the doors. You are asked to select a door. Not knowing which door the prize is behind, you pick one at random. Then the host points to one of the remaining doors and tells you that the prize is not behind that door. Now he asks you to pick one of the doors again, and this time you really will get the prize if it is behind the door, and will lose it if it is not.

Assuming that the host is telling the truth, and that the same thing would have happened no matter which door you picked, which of the remaining doors is more likely to have the grand prize behind it: the one you selected or the other door that the host didn't point out?

[Hurricane]

I saw that card trick earlier. You have to be pretty naive to be fooled by it.

[CyberGnu]

Urban, that was way to obvious. Bob ate the card. (Because he ran out of burgers.)

John, you should take the other door, since there is a 67% chance of that being the prize winning one.

[Dauphin]

Originally posted by Urban Ranger
This is interesting.

Check out this magic trick and see if you can figure out how it works.

I picked all the cards in one go and then they all disappeared - ands were replaced by other ones. Amazing!