Measurements are presented of the cross section for the production of at least four jets, of which at least two originate from $b$ quarks, in proton-proton collisions. Data collected with the CMS detector at the LHC at a center-of-mass energy of 7 TeV are used, corresponding to an integrated luminosity of 3 inverse picobarns. The cross section is measured as a function of the jet transverse momentum for p_\perp 20 GeV, and of the jet pseudorapidity for $|\eta|<2.4$ ($b$ jets) and 4.7 (untagged jets). The correlations in azimuthal angle and p_\perp between the jets are also studied. The $\eta$ and p_\perp distributions of the four jets and the correlations between them are well reproduced by event generators that combine perturbative QCD calculations at next-to-leading-order accuracy with contributions from parton showers and multiparton interactions.
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