Brain teaser thread

[Rogan Josh]

Yes of course! Well done!

Silly me...

[rah]

There are three switches in a room on the first floor and a lamp on the third floor. Each one is labeled On and Off. One (and only one) of the switches controls the lamp. There is no possible way for you to see whether the light is on or off from the first floor. You are alone in the house.


You are allowed to turn on and off the switches as often and as long as you'd like.
However, you can only go upstairs once to check on the status of the lamp.
Determine which switch controls the lamp.

[OPD]

Turn the first switch on and leave it for an hour then turn it off again.

then turn on the second switch and go upstairs.

if it's on it's the second one, if it's off but the bulb is warm it's the first switch otherwise it's the third one???

[rah]

Correct. What if it had been a neon lamp.


Your turn.

[OPD]

Originally posted by rah
Correct. What if it had been a neon lamp.


Your turn.

I guess I would have turned it on and off untill the bulb blew instead.

ok here's the only one I can think of.


Dave sells flour in quantities of 1 - 40 grams.
He buys a weighing scales to weigh out the flour and buys 40 weights ranging from 1 - 40 grams.

Smart Bob sees this and tells Dave that he didn't need to buy so many weights. For example he didn't need to buy a 5 gram weight as the 4 gram and 1 gram weight could have been used together, alternatively the 7 gram could have been placed on one side and the 2 gram weight placed on the other side to create a net weight of 5 grams.

Smart Bob then goes on to say that Dave needed only to buy 4 different weights.

What are the 4 weights which can be used to create net weights of all the values from 1 to 40???

[Zero-Tau]

1, 3, 9, 27.

1=1
2=3-1
3=3
4=3+1
5=9-3-1
6=9-3
7=9-3+1
8=9-1
9=9
etc.
(If you add a number, put the weight on the other side from the flour. If you subtract, put it on the same side.)

[rah]

1,3,9,27. That took a bit of trial and error. I'm sure there's a formula for it.

RAH

[Zero-Tau]

There is. First is 1, or 3^0. Then 3, or 3^1. Then 9, or 3^2. And finally 27, or 3^3.

Oh yeah, and I got it first.

[rah]

Yes, it was a crosspost, and you were first. When I started jotting you hadn't posted yet. Congrats.

Your turn.

I was just going to use the old classic from "DIE HARD with a Vengence" with the 5 gallon and 3 gallon container.

[Zero-Tau]

Naw, you do one. I'm leaving the forums now.

But...

I SHALL RETURN! Mwahahahaha!

(Yes, that was pointless.)

[rah]

The real teaser is getting this site to respond.

I'll go with the classic then.

You have a 5 gallon, a 3 gallon container and a pool of water. End up with exactly 4 gallons of water in the 5 gallon container, or the bomb blows up.

[Dauphin]

Fill the 5g from the pool.
Pour into 3g from 5g.
Empty 3g.
Pour into 3g from 5g.

Now there is 2g in the 3g container

Fill the 5g
Pour into 3g until full.

You now have 4g in 5g container.

[Urban Ranger]

Well, where's the question?

[Dauphin]

Oh right, its me is it? Err, give me a while to find/think of one.

While your waiting, anyone know the original reason for store items to be priced at just under a whole amount (e.g £9.99 as opposed to £10, or $4.95 instead of $5)?

And 'twasn't to make things look cheaper.

Edit - no to know. D'oh

[Dauphin]

Ok here is a nice and easy one...

Two men are paddling a rowboat. Suddenly the boat runs into something and comes to an abrupt stop. The man in the front of the boat gets thrown out of the boat. Although he hits nothing but water, when he climbs back into the boat, he is completely dry. How come?