In moment distribution method, the sum of distribution factors of all the members meeting at any joint is always 

Concept:

Distribution factor (DF):

\(DF={Stiffness\, of\, a\, member\over Sum\, of\, stiffness\, of \, all\, members\, at\, that \, joint}\)

Or

\(DF={Relative\, stiffness\, of\, a\, member\over sum\, of\, relative\, stiffness\, of \, all\, members\, at\, that \, joint}\)

Where M1, M2, M3, and M4 are moment induced in member OA, OB, OC, and OD respectively.

The summation of DF for all members at a joint is one.