A pion is an unstable particle that has an average lifetime of 2.55 10-8 s.

A pion is an unstable particle that has an average lifetime of 2.55 × 10-8 s. This is the time interval between its creation in a nuclear process and its extinction into decay products, as measured in a frame of reference at rest with respect to the pion. An "average" pion is traveling at 0.310c relative to Earth. How far does it travel in its lifetime, relative to Earth?