A muon is an unstable elementary particle with an average lifetime of 2.20×10-6 seconds (from the moment of creation until it decays) as measured by an observer at rest with the muon. If an average muon travels a distance of 900 meters during one lifetime, according to an observer in the laboratory, what is the muon's speed (in m/s)? I have the Lorentz Transformations sitting right in front of me but I can't seem to make the logical jump again. If O is the observer's frame and O' is the muon's frame of reference I have the following data: x = ? t = 2.2*10^6s x' = 900m t' = ? I really don't remember where to go from here. I tried taking the ratio of x to t and x' to t' the Lorentz transformations but it didn't yield anything relevant. Thanks in advance.