Toolkit 70

Geometric Approach in Probability

1 dimension

0x10\le x\le 1
P ⁣(13<x<12)=1213=16P\!\left(\tfrac{1}{3}<x<\tfrac{1}{2}\right)=\tfrac{1}{2}-\tfrac{1}{3}=\tfrac{1}{6}
Number line from 0 to 1 with segment between 1/3 and 1/2 highlighted

2 dimensions

0x,y10\le x,y\le 1
P(xy12)=2×12×122=14P(|x-y|\ge \tfrac{1}{2})=2\times\frac{\tfrac{1}{2}\times\tfrac{1}{2}}{2}=\tfrac{1}{4}
Unit square with two shaded triangles representing |x-y| >= 1/2

3 dimensions

0x,y,z10\le x,y,z\le 1
P(x+y+z1)=12×12×123=16P(x+y+z\le 1)=\frac{\tfrac{1}{2}\times\tfrac{1}{2}\times\tfrac{1}{2}}{3}=\tfrac{1}{6}
Unit cube with tetrahedron representing x+y+z <= 1 shaded