The branching ratio of beauty hadrons to final states containing two charm hadrons, Br(b--> DDbarX), has been measured using an inclusive method in hadronic Z decays with the OPAL detector at LEP. The impact parameter significance of tracks opposite tagged b-jets is used to differentiate b--> DDbarX decays from other decays. The result is
Br(b--> DDbarX) = (10.0 +- 3.2 (stat)^{+2.4}_{-2.9}(det)^{+10.4}_{-9.0}(phys)),
where ``det'' is the systematic uncertainty due to the modelling of the detector, and ``phys'' is the systematic uncertainty due to the modelling of the underlying physics. Using this result, the average number of charm plus anti-charm quarks produced in a beauty quark decay, n_c, is found to be 1.12^+0.11_-0.10.