Thursday, July 30, 2009

Question Time.

Here is another previously unpublished post. It's actually a test that I saw elsewhere which I found quite interesting, so if anyone wants to try and answer it, feel free:
Only one of the following assertions is true about a particular hand of cards:
There is a king in the hand, or an ace, or both.
There is a queen in the hand, or an ace, or both.
There is a jack in the hand, or a ten, or both.
Is is possible that there is an ace in the hand?
I'll put the answer and explanation of why it is interesting up later.

12 comments:

Mark Wadsworth said...

After a life time of doing silly puzzles, my knee-jerk response is that the answer is "No".

JuliaM said...

Argh! These things cause me brain-lock..! :)

klingsor said...

No it's not possible. If there were an ace in the hand then both the first two statements would be true. But we are told that only one of them is. QED

Ross said...

Both Mark and Klingsor are correct.

When the question was first tried out on Princeton students 99% of them got it wrong.

the answer is here along with an explanation of why people normally get it wrong despite its seeming simplicity.

Ross said...

Sorry that was an expired link, try this.

Matthew said...

I got your question, but I don't understand (from the link) this one:

----
If there is a king in the hand, then there is an ace in the hand.
If there isn't a king in the hand, then there is an ace in the hand.

One of these statements is true and the other false.
----

they say this means that there isn't an Ace in the hand. But why? If the first is true, and the second false, and there is a King in the hand, isn't there also an Ace in the hand?

Ross said...

That is confusing and I can't understand it yet after half an hour of trying to figure it out.

Matthew said...

Mmm, page 180 of this explains it in more detail plus (what I actually added myself) 'There is a King'.

Apparently the point is that there might not be an Ace in the hand (presumably if the first statement is false and the second true), which is obviously rather different from the previous link which seems to be asserting there can't be an Ace in the hand, I think.

Matthew said...

http://books.google.co.uk/books?id=ujoNZNZrZcoC&dq=%22if+there+is+a+king+then%22&source=gbs_navlinks_s

Ross said...

"Mmm, page 180 of this explains it in more detail plus (what I actually added myself) 'There is a King'. "

If there is a missing part of the question that explains a lot.

TheFatBigot said...

If there is an ace then the first and second statements are both true. We are told that only one of the three statements is true, therefore there can't be an ace.

Unless I'm wrong.

Ross said...

You are correct.