Two points are placed randomly along the circumference of a circle. What is the probability that the chord drawn between them is longer than the radius of the circle?
How often is Length of Chord > Radius?
by
Vijay Simha
A positive integer \(n\) has \(d\) positive divisors.
After doubling \(n,\) you find that \(2n\) has \(2d\) positive divisors.
Is it possible that after tripling \(n,\) you will find that \(3n\) has \(3d\) positive divisors?
by
Pi Han Goh
The atmosphere is a layer of gas that surrounds our planet and is several hundred kilometers thick. Its main components are nitrogen, oxygen, argon, and water vapor.
What is the approximate mass \(m\) of the entire Earth's atmosphere?
Details and Assumptions:
- The circumference of the Earth is about \(40,000 \text{ km}.\)
- Gravitational acceleration is approximately \(10 \text{ m/s}^2.\)
- The mean air pressure on the Earth's surface is about \(1 \text{ bar } \big(\SI{1}{bar} = \SI{10^5}{Pa} \big).\)
by
Markus Michelmann
Define the star operation as \(a\star b=a+ab+b.\)
Then define the star power operation as \(a^{\star n}=\underbrace{a\star a\star a\star\cdots\star a}_{a\, \mathrm{written} \, n \, \mathrm{times}},\) with \(a^{\star 1}=a.\)
What is \(7^{\star7}?\)
by
Steve Gualtieri
An equilateral triangle and 2 other regular polygons share a single vertex in such a way that the three shapes completely cover the \(360^\circ\) of space surrounding the vertex without overlapping.
What is the largest possible number of sides that one of the regular polygons can have?
An equilateral triangle, regular 9-gon, and regular 18-gon can cover all \(360^\circ\) around a single vertex. Is 18 the maximum number of sides one of these regular polygons can have?
by
David Vreken