Author: xi'an

operation precisely impossible

Since the solution to the previous riddle from The Riddler on the maximum of  different terms in the composed operation a∅b∅c∅d∅e∅f depending on the bracketing ordering and the meaning of...continue reading.

operation impossible

A riddle from The Riddler on how many different numbers one could at most produce from six initial values and the four basic operations. In other words, how many values...continue reading.

StanCon 2023 [20-23 July 2023]

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alone in Napoli

A combinatorics puzzle from The Riddler about a Napoli solitaire where 4 x 10 cards numbered from 1 to 10 are shuffled and the game is lost when a number...continue reading.

The Effect [book review]

While it sounds like the title of a science-fiction catastrophe novel or of a (of course) convoluted nouveau roman, this book by Nick Huntington-Klein is a massive initiation to econometrics...continue reading.

latest math stats exam

As I finished grading our undergrad math stats exam (in Paris Dauphine) over the weekend, which was very straightforward this year, the more because most questions had already been asked...continue reading.

Tribonacci sequence

A simplistic puzzle from The Riddler when applying brute force: A Tribonacci sequence is based on three entry integers a ≤ b ≤ c, and subsequent terms are the sum...continue reading.

foliage to the max

An easy riddle from The Riddler that did not even require coding! Given that a tree changes colours at a random time A distributed according to a Uniform distribution (over...continue reading.

optimal leap year

A riddle about leap years: a solar year consists of approximately 365.24217 mean solar days, which is why there is a leap year approximately every four years. Approximately because the...continue reading.

another drawer of socks

A socks riddle from the Riddler but with no clear ABC connection! Twenty-eight socks from fourteen pairs of socks are taken from a drawer, one by one, and laid on...continue reading.