Archive for May, 2010

Where is my wife?

Monday, May 31st, 2010

My wife goes to the super market while I first go to the bank. When I later go to the super market to find her, I can not.

The super market has aisles laid out in a grid with three columns and twelve rows. I enter the super market in the lower right corner. She is moving in a random fashion, three times slower than me.

What is my best strategy for finding her?

I could call her on her cell phone, but she never turns it on. My best bet is to walk down the aisles looking left and right at every junction. Sometimes this approach requires half an hour, so my question is: how should I move?


Monday, May 31st, 2010

Science is a procedure for testing and rejecting hypotheses, not a compendium of certain knowledge. – Stephen Jay Gould


Sunday, May 30th, 2010

Lucia de Berk is a Dutch nurse who has spent six years of a life sentence in jail for murdering seven people in a killing spree that never happened. She will hear about her appeal on Wednesday, and there is now little doubt that she will be cleared. The statistical errors in the evidence against her were so crass that they can be explained in one newspaper column. So will the people who jailed her apologise? – Read more

Richard D Gill has written a lot about the fiasco:

  1. Elementary statistics on trial (one in twenty-five innocent nurses go to jail (joint with P. Groeneboom; preliminary version)
  2. On the (ab)use of statistics in the legal case against the nurse Lucia de B, preprint at, final version published (with discussion by David Lucy) in Law, Probability and Risk, 2007, joint with Marieke Collins, Michiel van Lambalgen, Ronald Meester.
  3. Lucia talk at Vierhouten hackers conferencee Lies damned lies and legal truths
  4. Astin day presentation: a story in a story Statistics and Ethics (Dutch outside, English inside)
  5. Lies, damned lies, and legal truths (2009), prepublication
  6. Remarks on the Lucia data – why the numbers keep changing (2009)

Wikipedia article.

Playful thinking

Saturday, May 29th, 2010

Slide the grid squares around so that they all join up into a single connected network with no loops. Click on the arrows at the edges of the grid to move a row or column left, right, up or down. The square that falls off the end of the row comes back on the other end. Squares connected to the middle square are lit up. Aim to light up every square in the grid (not just the endpoint blobs). Connecting across a red barrier line is forbidden. On harder levels, there are fewer barriers, which makes it harder rather than easier!

Play it here.

48 is not a square number

Friday, May 28th, 2010

– Did you know that 49 is a square number?
– That is what my postman claims. Personally I have no idea.
– How old is your postman?
– 48.
– Interesting!
– He says 48 is not a square number.
– But what about 4489?
– What about it?
– Is it a square number?
– I have to ask him.
– Ask him also about 444889 and 44448889.
– Are you suggesting that all numbers on the form 4 444…444888…888 9 are squares?
– I am suggesting you should invite your postman for a cup of tea.

Problem source: Mattenøtter, Teknisk Ukeblad.


Friday, May 28th, 2010

It is the instinct of understanding to contradict reason. – Friedrich Jacobi

Is 7 lucky?

Thursday, May 27th, 2010

– 4 is a lucky number since 1/2 + 1/2 = 1 and 2 + 2 = 4.
– Give me another example.
– 11 is also lucky since 1/2 + 1/3 + 1/6 = 1 and 2 + 3 + 6 = 11.
– Is 7 lucky?
– While you’re at it, can you find all unlucky numbers?

Problem source: Past Fortnight Problems.


Thursday, May 27th, 2010

Great teachers turn ‘cant’s’ into can openers. – N. Wylie Jones


Wednesday, May 26th, 2010

Last night I went home on the local bus and couldn’t help overhearing a conversation between two elderly women.

– My grandson is 31 years old tomorrow.
– Say congratulations from me.
– I will if I remember it.
– Your memory is failing you?
– Sometimes I feel like being 331 years old.
– That is strange!
– Do you feel the same way?
– No, not that. I just noticed that 31 and 331 are both prime numbers.
– Maybe just a coincidence.
– Maybe not. I just discovered that 3331 is a prime too.
– How on earth did you discover that?
– In the book I always carry with me.
– Which book?
– “Primes for any occasion,” by Mary Lamb.
– What about 33331? What does Mary say about that.
– It is a prime too!
– I wonder if all numbers on the form 333…3331 are primes.
– I think they are.
– Why?
– That is my stop. Goodnight.

Problem source: mathsbyemail.


Wednesday, May 26th, 2010

Truth exists.  Only lies are invented. – George Braque