The first measurement of the cross section ratio (\sigma_{t\overline{t}b\overline{b}}) / (\sigma_{t\overline{t}jj}) is presented using a data sample corresponding to an integrated luminosity of 19.6 fb⁻¹ collected in pp collisions at (\sqrt{s})=8TeV with the CMS detector at the LHC. Events with two leptons (e or (\mu)) and four reconstructed jets, including two identified as b quark jets, in the final state are selected. The ratio is determined for a minimum jet transverse momentum (p_T) of both 20 and 40 GeV/ c. The measured ratio is 0.022±0.003(stat)±0.005(syst) for (p_T)>20 GeV/c. The absolute cross sections (\sigma_{t\overline{t}b\overline{b}}) and (\sigma_{t\overline{t}jj}) are also measured. The measured ratio for (p_T)>40 GeV/c is compatible with a theoretical quantum chromodynamics calculation at next-to-leading order.