Atmospheric dust particles around construction sites cause environmental problems. The number of particles in a unit volume is modeled as a Poisson distribution with unknown parameter lambda. 50 small air samples were collected containing a total of 2500 particles. The maximum likelihood estimate of lambda is calculated as 2500/50 = 50. In traffic engineering, the time intervals between vehicles passing a point are exponentially distributed with unknown parameter lambda. For 30 observed intervals with a mean of 0.55 minutes, the maximum likelihood estimate of lambda is calculated.