The riddler is a weekly math, logic and probability problem hosted by fivethirtyeight.com, a statistically oriented politics, sports and culture blog.
If the answer is particularly cool or my solution can be extended, made interactable or generalized then I'll usually write it up. I've also created and submitted some problems that have been featured.
This is a mathmatical object I made and obviously named after myself
It is a square matrix such that each row's leftmost element times its rightmost element will equal the two inner numbers (in the example below, the top row has 6*7 = 42). Similarly, each column's uppermost element times the column's lowermost element equals the middle digits (in the example, the right column is 7*8 = 56), as read top to bottom.
6 4 2 7
4 2 0 5
8 4 8 6
8 6 4 8
4 x 4 Barron Square
This was then expanded on to be a 8x8 with two digit rows/columns being multiplied to get four digit products
This is a problem about finding geometric subshapes and summing their areas
The largest circle below has a radius of 10, the medium circle has a radius of 5 and the small, orange circle has a radius of 2. The orange circle crawls counterclockwise along the edge of the largest circle until it meets the medium circle, at which point it crawls up along the edge of the medium circle until it reaches the crest. What is the area of the shaded orange region in the right image?
This is a problem about coloring a square so if a 2x2 section is snipped out you know where it was originally located
You are given an empty 4-by-4 square and one marker. You can color in the individual squares or leave them untouched. After you color as many or as few squares as you’d like, I will secretly cut out a 2-by-2 piece of it and then show it to you without rotating it. You then have to tell me where it was (e.g., “top middle” or “bottom right,” etc.) in the original 4-by-4 square.
Can you design a square for which you’ll always know where the piece came from?
This problem is about reducing ambiguity in seven-display segments
Given a two-character, seven-segment display, like you might find on a microwave clock, how many numbers can you make that are not ambiguous if the display happens to be upside down?
For example, the number 81 on that display would not fit this criterion — if the display were upside down it’d appear like 18. The number 71, however, would be OK. It’d appear something like 1L — not a number.
This problem was about creating triangles in a unit circle and determining if the circle's center was enclosed.
Choose three points on a circle at random and connect them to form a triangle. What is the probability that the center of the circle is contained in that triangle?
This led to the following visualization:
Results from 2d simulation
This was followed up by the 3d case:
Choose four points at random (independently and uniformly distributed) on the surface of a sphere. What is the probability that the tetrahedron defined by those four points contains the center of the sphere?
Results from 3d simulation
The probability that the shapes would enclose the center resulted in surprisingly nice 25% and 12.5%
This problem was about taking a state map, show below, and gerrymandering it as much as you could.
Below is a rough approximation of Colorado’s voter preferences, based on county-level results from the 2012 presidential election, in a 14-by-10 grid. Colorado has seven districts, so each would have 20 voters in this model. What is the most districts that the Red Party could win if you get to draw the districts with the same rules as above? What about the Blue Party? (Assume ties within a district are considered wins for the party of your choice.)
We used a randomized search that would try to slightly move districts, check continuity and then check the voting results. The method resulted in uniquely shaped maps that optimized each side's winningness.