P\left( x \right) = \frac{{e^{ - \lambda } \lambda ^x }}{{x!}}
% MathType!MTEF!2!1!+-
% feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
% 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY-Hhbbf9v8qqaqFr0xc9pk0xbb
% a9q8WqFfeaY-biLkVcLq-JHqpepeea0-as0Fb9pgeaYRXxe9vr0-vr
% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiaadcfadaqada
% qaaiaadIhaaiaawIcacaGLPaaacqGH9aqpdaWcaaqaaiaadwgadaah
% aaWcbeqaaiabgkHiTiabeU7aSbaakiabeU7aSnaaCaaaleqabaGaam
% iEaaaaaOqaaiaadIhacaGGHaaaaaaa!429D!
Pasting the above "text" into MathType 5.0 will enter the above equation and make it possible to edit, save, and use in applications such as MS Word.