Author: xi'an

parking riddle

The Riddler of this week had a quick riddle: if one does want to avoid parallel parking a car over a six spot street, either the first spot is available...continue reading.

Fermat’s Riddle

·A Fermat-like riddle from the Riddler (with enough room to code on the margin) An  arbitrary positive integer N is to be written as a difference of two distinct positive...continue reading.

Le Monde puzzle [#1157]

The weekly puzzle from Le Monde is an empty (?) challenge: Kimmernaq and Aputsiaq play a game where Kimmernaq picks ten different integers between 1 and 100, and Aputsiaq must...continue reading.

Le Monde puzzle [#1155]

The weekly puzzle from Le Monde is another Sudoku challenge: Anahera and Wiremu play a game for T rounds. They successively pick a digit between 1 and 3, never repeating...continue reading.

where is .5?

A Riddler’s riddle on breaking the unit interval into 4 random bits (by which I understand picking 3 Uniform realisations and ordering them) and finding the length of the bit...continue reading.

the limits of R

It has been repeated many times on many platforms, the R (or R⁰) number is not a great summary about the COVID-19 pandemic, see eg Rossman’s warning in The Conversation,...continue reading.

le compte est bon

The Riddler asks how to derive 24 from (1,2,3,8), with each number appearing once and all operations (x,+,/,-,^) allowed. This reminded me of a very old TV show on French...continue reading.

Riddle of the lanes

An express riddle from the Riddler about reopening pools, where lanes are allowed provided there is no swimmer in the lane or in any of the adjacent lanes. If swimmers...continue reading.

sans sérif & sans chevron

{\sf df=function(x)2*pi*x-4*(x>1)*acos(1/(x+(1-x)*(x<1)))} As I was LaTeXing a remote exam for next week, including some R code questions, I came across the apparent impossibility to use < and > symbols in...continue reading.

overlap, overstreched

An interesting challenge on The Riddler on the probability to see a random interval X’ing with all other random intervals when generating n intervals from Dirichlet D(1,1,1). As it happens...continue reading.

a new Monty Hall riddle

The Riddler was sort of feeling the rising boredom of being under lockdown when proposing the following variant to the Monty Hall puzzle: There are zero to three goats, with...continue reading.