Mathematik
12 cards from across every topic, each citing a source. Tap one to open it in the feed.
- "Arabic numerals" are an Indian invention.
The signs 0 to 9 emerged in India between the 1st and 4th centuries, the place-value system around 600. Arab and …
- 23 people in a room, and two probably share a birthday.
With just 23 people, the chance that two share a birthday already exceeds 50 %. With 50 people it's 97 %. Intuition …
- Check the units before you trust the number.
Every meaningful physical equation has the same units on both sides: metres stay metres, seconds stay seconds. If your …
- Fold a sheet of paper 42 times and you reach the Moon.
A sheet of paper is 0.1 millimetres thick. Every fold doubles the thickness. After 10 folds it's 10 centimetres, after …
- How a ZIP file shrinks without losing a single bit.
Two tricks. First, the algorithm replaces repetitions with a back-reference: 'same as 200 characters ago, 15 characters …
- How a computer rolls dice when all it can do is calculate.
A computer knows no chance. It starts with a number, the seed, and runs it through a formula; each result becomes the …
- How many piano tuners are in Chicago? Work it out.
Enrico Fermi estimated unknowns by breaking them into quantities he roughly knew: population, households, pianos per …
- How to count to 31 on one hand.
In binary, each digit is worth twice the one before it: 1, 2, 4, 8, 16. The number 1011 means 8 + 0 + 2 + 1 = 11. Your …
- The word algorithm is a man's name.
Muhammad ibn Musa al-Khwarizmi worked in 9th-century Baghdad. His book on calculation appeared in Latin as "Algoritmi …
- Three doors, one car: why switching doubles your odds.
A car sits behind one of three doors. You pick one; the host, who knows where the car is, opens another door showing a …
- Why giant movie ants would collapse on the spot.
Double a body's size and its surface area quadruples, but its volume and weight increase eightfold. Legs support weight …
- Zero as a number is only 1,400 years old.
Earlier systems knew zero at most as a placeholder; Roman numerals didn't even have that. In 628, the Indian …