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June 9th, 2014, 10:15 PM  #1 
Senior Member Joined: Nov 2013 Posts: 160 Thanks: 7 
This math question from an admissions test for an elementary school in Hong Kong is going viral in China. According to ChinaSmack, it was the secondmostpopular post on Chinese microblogging site Sina Weibo on June 5, when it was published. The question was part of an admissions test for firstgraders. They had 20 seconds to answer. Can you solve it? From Sina Weibo: "What takes an elementary school student just seconds to do; takes a high school student several minutes; takes a college student half and hour and up; and takes a Ph.D a lifetime…" Last edited by skipjack; April 16th, 2015 at 05:54 PM. 
June 10th, 2014, 05:57 AM  #2 
Member Joined: May 2014 From: India Posts: 87 Thanks: 5 Math Focus: Abstract maths!  Solved it easy!
Maybe I'm an elementary school student. It's quite simple. Look at it upside down because the car parks that way. Answer is L8, which is upside down for 87. :P
Last edited by skipjack; June 11th, 2014 at 09:07 AM. 
June 10th, 2014, 07:28 AM  #3  
Senior Member Joined: Nov 2013 Posts: 160 Thanks: 7  Quote:
I admit, for me it took a little more than 20 seconds. But I am not an elementary school student.  
June 10th, 2014, 11:07 PM  #4 
Senior Member Joined: Apr 2014 From: UK Posts: 954 Thanks: 342 
Well, it turns out I was studying for a PhD and didn't even know it! edit: typo 
June 11th, 2014, 04:48 AM  #5 
Member Joined: May 2014 From: India Posts: 87 Thanks: 5 Math Focus: Abstract maths! 
Thus one teaches a very important lesson. Sometimes we foolishly assuming things as complex and burn our brains out when actually it may be in fact be very simple. I did it fast. I knew it could not be a series because it was for grade one and your quote from ChinaSmack explicitly tells that. Using common sense (not pen and paper), it is easy to think that successive numbers only form car parking slots. And then suddenly it struck me! It is a wonderful question. Highly stimulative. 
June 11th, 2014, 06:11 AM  #6 
Math Team Joined: Apr 2010 Posts: 2,780 Thanks: 361 
My strategy was: how can these numbers differ by 1 or 2 from left to right or right to left. I see I was not alone there 
June 11th, 2014, 06:23 AM  #7 
Senior Member Joined: Nov 2013 Posts: 160 Thanks: 7 
I almost gave up after one minute. It was irritating for me why there is number 06 in a wrong slot if the numbers are in increasing order. Nevertheless I just randomly chose the number 90 for the empty slot because it seemed appropriate if the numbers were in increasing order, and I noticed that it is the same as 06 turned upside down, and then I immediately saw the solution. I would say that my strategy was trial and error. It took me more than one minute, but it was just a lucky guess by myself. Otherwise I could have given up, because it seemed hopeless. 
June 11th, 2014, 08:58 AM  #8 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1038 
?,M,T,W,T,F,? After an hour: Jack Adult says "I quit"! After 23 seconds: Li'l John Child says "Sunday, Saturday" 
June 11th, 2014, 09:06 AM  #9 
Global Moderator Joined: Dec 2006 Posts: 20,927 Thanks: 2205 
The answer is 87. Why would one give it upside down?

June 11th, 2014, 10:48 AM  #10 
Senior Member Joined: Nov 2013 Posts: 160 Thanks: 7 
I got another puzzle. It is taken from the book Higgs Force by Nicholas Mee. The question is: What shape goes in the empty square in the grid shown below? 

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