I am speaking about the psychology of dreams at the British Science Festival 2012 in Aberdeen at the weekend. Do come along and say hi. Details here.

OK, here is the puzzle. As ever, please do **NOT** post your answers, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

If you turn this number upside down or reflect it left-to-right you get 11 either way, but the original number is not 11. What is it?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called **PUZZLED** and is available for the **Kindle** (UK here and USA here) and on the **iBookstore** (UK here in the USA here). You can try 101 of the puzzles for free here.

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Quite quick to get an answer, whether it’s the right answer or not, will find out Monday!

Took me just a little less than 11 seconds (if my answer is right ;-) )

your 11 seconds leading me to the “intendet” solution… (if the answer is right…)

Cue sumg “Got it in less than X seconds” comments

How come you didn’t delete this spoiler, Richard?

IX

Too late. Haha!

2 answers, both correct in 2 seconds

Embarrassed – nearly an hour to get this one :0s

I got an answer in 5 sec onds, whether that answer turns out to be correct…

There are 10 types of people on this planet – those that understand binary and those that do not

I guess it depends on the meaning or indeed meanings of “11”.

I got one answer and a dodgy second answer. Reading the comments gets a third.

Hmmm got an answer I’m not happy with very quickly. Browsing the comments I see another I’m even less happy with. With recent track record, thinking the answers rubbish will certainly not discount it from being the one given on Monday.

Yeah, type of thing.

The answer is pretty good. Best one in a long time I’d say even though I got it in a few seconds, it’s the type of thing that you could easily miss.

Type of thing?

Why is my answer so much more banoffe than binary ?

There is only one answer and it’s much simpler than some of these comments would suggest.

I’ve got a good answer which is nothing to do with binary, and I don’t get the comments ’11’ in binary is 3, so what’s that got to do with anything?

My answer also isn’t in binary, it will be exciting to see on monday what people thought they had…

I have two answers. The first one, which I think is the one you will reveal on Monday only took a few seconds to get. The second answer I got after reading some of the comments – it is also correct given the way the question is phrased.

About a nanosecond – before I’d finished reading the question, in fact. Always assuming I’m right, of course…..

It took me about 5 minutes, but I am not sure if it is right or not. It depends a little on what “turn it upside down” means. My answer doesn’t work if it means a mirror reflection, but if it means writing the answer on a piece of paper and turning it through 180 degrees it works

Exactly the same answer I found

Thought about for a couple of minutes – couldn’t see the answer. Dozed, woke up and saw the answer straight away.

Ah, Mr Wiseman, you are a rotter!! Took me about a minute – good one.

It took 4.3 seconds to come up w/an answer. It took a full minutesnd a half trouble convince myself the answer was too easy and that I have an 83.8% chance of being wrong.

1 sec to find the answer……:)

Think I’ve got it; 3 false starts & then “ahhhhh”. About 5 min.

I got an answer almost immediately. Whether it is correct or not will have to wait until Monday!

The problem says “If you turn this number upside down or reflect it left-to-right you get 11 either way, but the original number is not 11. What is it?” Does Richard mean that the number in question is represented as “11” or that “11” is the number “eleven”?

It is the actual number eleven in both cases.

My interpretation is that Richard’s first “11” means the integer between ten and twelve. The second “11” means the symbol “11”.

There is another solution as well if you interpret the question differently. Again you have to ascribe two different meanings to the symbol “11” in the question to make it work.

In other words it is a trick question.

I see what you mean now Match.

i now how three answers, with my third being the one I expect RW to post.

The comment below about the clear wording of the question helped.

My other two answers and my comments are still acceptable within the normal parameters of WisemanWorld.

Took me about 4 seconds to come up with an infinete amount of correct answers

It took me about 4 seconds to come up with an infinite amount of correct answers

9 secs to get an answer then 9 mins trying to make sense of the comments,

I can also do it ‘by moving just one of the matchsticks’

Instantly this time. The clear wording of the question helped.

I think the wording ‘…turn this number upside down…’ is ambiguous as it does not say about which axis the rotation should be made. Rotation about an axis normal to the plane of the screen gives a different result to rotation about a horizontal or vertical line on the screen.

Does “Spoiler + Spoiler” count as a spoiler?

Julius caesar would know immediately.

II = 2 in Latin. Any Roman knows that whether it’s upside down, or right side up, or rotated left or right. SPQR