How did you get on with this week’s puzzle post ? Here are the answers ... and another puzzle, just in case two weeks seems like too long a wait between puzzles! 
 
 I hope you enjoyed solving today’s odd-one-out problem, because it was meant to be funny, as well as fun. 
 
 Puzzle maven Tanya Khovanova, who devised it, intended it to be taken that way. Tanya - like many of you who posted comments - does not like odd-one-out puzzles. 
 
 Let’s see why with another puzzle. Which animal is the odd one one out? 
 
 Pig 
 
 Cow 
 
 Hen Sheep 
 
 The standard answer is hen, since it is the only bird. But what about sheep, the only word with more than three letters? Or pig, the only non-kosher animal? Or cow, the only word where the letters are in alphabetical order? 
 
 
 
 Tanya’s point is this: odd-one-out puzzles penalize creative thinking. And that makes them self-defeating, since the point of a puzzle is to encourage creative thinking. 
 
 “Suppose you are going for a cup of coffee,” she says. “Who would you rather invite along: the person who answers correctly or someone who comes up with a creative ‘wrong’ answer? Multiple-choice questions check standard reasoning, but punish non-triviality and originality.” 
 
 So Tanya devised a puzzle that is a subtle protest against odd-one-out puzzles. 
 
 Have a look at it again in the illustration above. 
 
 At first glance, the odd-one out is the only green one. 
 
 But what about the only circle? 
 
 Or the only small square? 
 
 Or the only one with no border? 
 
 By a process of elimination we realize that the odd one out is the leftmost figure because it is the only one that is not an odd one out! 
 
 The leftmost figure is special because it is not special. It shares redness, squareness, size and border with other shapes. 
 
 However, if someone can come up with a brilliantly non-trivial and original wrong answer I will also accept it - please post your suggestions below! 
 
 The second puzzle is also visual. 
 
 And here’s a tip. Whenever you are asked to solve a puzzle in an extremely short amount of time, such as 20 seconds in this case, you can usually deduce that the answer is incredibly simple. 
 
 The sort of answer a six year old would be able to come up with. The time constraint is urging you to UNDERTHINK the problem. 
 
 Turn the image upside down and you will see the answer: 87. 
 
 This question, in fact, contains another puzzle within it - one that I was only made aware of this afternoon. 
 
 Legendary British puzzle inventor David Bodycombe got in touch to tell me that the Hong Kong puzzle is one of his. He came up with the idea while in a car park in Portugal two decades ago and published it in a 2002 IQ puzzle book for Marks & Spencer. 
 
 He has no idea whether or not it was used in a Hong Kong school test - and if it was he didn’t receive a penny! 
 
 Now for a bonus question in a similar vein, which I first spotted years ago (and which took me longer than it should!). 
 
 This one you’re going to have to do on your own. Or ask a three-year-old. 
 
 If you’d like to see a video of me solving the original two puzzles, just click below: 
 
 Tanya Khovanova writes a brilliant puzzle blog. 
 
 I post a puzzle here on a Monday every two weeks. If you like this sort of thing check out my other Guardian blog Adventures in Numberland. You can also check me out on Twitter, Facebook, Google+ and my personal website. 
 
 
 
 I have now featured maths puzzles from Singapore, Vietnam and Hong Kong schools. If you know of a great puzzle from South Korea, Mongolia or Laos please get in touch. 
 
 
 
 
 
 
 
 ||||| Hello guzzlers. 
 
 Welcome to the second instalment of my new puzzle series. 
 
 Last time I asked you about Denise and her birthday. Today it’s a totally different style of problem 
 
 In colour! 
 
 Look at the image above. Which is the odd one out and why? 
 
 
 
 You want more? 
 
 Okay, here’s a second puzzle. It’s from the first grade admissions test for the Hong Kong Elementary School. So it’s for six year olds. 
 
 
 
 It went viral a year ago - but many of you will not have seen it. 
 
 Which parking spot number is the car parked on? 
 
 Can you solve it in 20 seconds, as the children were expected to do? 
 
 Twenty seconds is all you get ... 
 
 I’ll be posting the answers on this blog later today. If you’d prefer to watch the video of this problem, here it is: 
 
 Sorry, your browser is unable to play this video. Facebook Twitter Pinterest 
 
 Odd-one-out puzzle devised by Tanya Khovanova. 
 
 
 
 I post a puzzle here on a Monday every two weeks. If you like this sort of thing check out my other Guardian blog Adventures in Numberland. You can also check me out on Twitter, Facebook, Google+ and my personal website. 
 
 If you create puzzles and fancy seeing one published here get in touch. ||||| Exclusive: all was well with Albert, Bernard and Cheryl until Denise showed up ... that’s right, it’s another birthday brainteaser from Singapore 
 
 Cheryl's birthday puzzle part two, Denise's revenge - can you solve it? 
 
 Welcome to the first of my new puzzle series. Every second Monday I’ll be posting some kind of brainteaser, usually mathematical, here on the science blog network. 
 
 I’ll be posting the solution on Tuesdays. Which gives you the Guardian puzzlers – guzzlers, obviously! – a full day to chew, digest, absorb and solve. 
 
 To kick the series off, we have the puzzle that the entire world has been waiting for. 
 
 Remember the Albert, Bernard and Cheryl problem – also known as the Cheryl’s birthday problem? It exploded across the internet last month, becoming the most discussed logic puzzle of recent years. 
 
 The puzzle was written by Joseph Yeo Boon Wooi of Singapore’s National Institute of Education, originally for a test paper in the Singapore and Asian Schools Math Olympiad. 
 
 Well, Dr Yeo has written a sequel and I’m thrilled that he has given it to me for the launch of this series. A new character joins logic’s most famous threesome. Enjoy! 
 
 Albert, Bernard and Cheryl became friends with Denise, and they wanted to know when her birthday is. Denise gave them a list of 20 possible dates. 
 
 17 Feb 2001, 16 Mar 2002, 13 Jan 2003, 19 Jan 2004 
 
 13 Mar 2001, 15 Apr 2002, 16 Feb 2003, 18 Feb 2004 
 
 13 Apr 2001, 14 May 2002, 14 Mar 2003, 19 May 2004 
 
 15 May 2001, 12 Jun 2002, 11 Apr 2003, 14 Jul 2004 
 
 17 Jun 2001, 16 Aug 2002, 16 Jul 2003, 18 Aug 2004 
 
 Denise then told Albert, Bernard and Cheryl separately the month, the day and the year of her birthday respectively. 
 
 The following conversation ensues: 
 
 Albert: I don’t know when Denise’s birthday is, but I know that Bernard does not know. 
 
 
 
 Bernard: I still don’t know when Denise’s birthday is, but I know that Cheryl still does not know. 
 
 
 
 Cheryl: I still don’t know when Denise’s birthday is, but I know that Albert still does not know. 
 
 
 
 Albert: Now I know when Denise’s birthday is. 
 
 
 
 Bernard: Now I know too. 
 
 
 
 Cheryl: Me too. 
 
 
 
 So, when is Denise’s birthday? 
 
 
 
 To clarify: neither Albert, Bernard or Cheryl know anything else at the start apart from the fact that Albert has been told the month, Bernard the day (meaning the number of the day), and Cheryl the year. 
 
 Extra points: a playful aspect of the Cheryl birthday problem was that the answer - i.e. Cheryl’s birthday - is also Dr Yeo’s birthday. He has also hidden a fun little nugget - what he calls an “Easter egg” - in this one. It is something purely mathematical. What is it? 
 
 Go, guzzlers, go! 
 
 Facebook Twitter Pinterest As well as being the creator of the Cheryl puzzle, Joseph Yeo Boon Wooi also stands out in the mathematical community for the large number of o’s in his name. Photograph: Joseph Yeo Boon Wooi 
 
 My latest book is Alex Through the Looking Glass (UK) and The Grapes of Math (US). To keep in touch with this blog I’m on Twitter, Facebook and Google+. Also, my personal website.
– Last month the Internet went nuts trying to figure out Cheryl's birthday. Today, Alex Bellos is back in the Guardian with two more stumpers, what he calls the "second installment" in his let's-drive-everyone-mad puzzle series (the first was a sequel to the Cheryl's birthday puzzle). The reason it comes with the title "Are you smarter than a Hong Kong six-year-old?" is that Bellos actually took the first puzzle from an admissions test for first grade in Hong Kong. You only have 20 seconds to solve it, just like the schoolkids did. Got it? We'll direct you to the answer, but not before you head to the Guardian to view the second visual doozy. All you have to do there is figure out which shape is the odd one out. Answers to both here. (Click to read about the Internet's most mysterious puzzle.)