  A measurement of the ratio of the inclusive 3-jet to 2-jet cross sections as
a function of the total jet transverse momentum, HT, in the range 0.2 < HT <
2.5 TeV is presented. The data have been collected at a proton-proton
centre-of-mass energy of 7 TeV with the CMS detector at the LHC, and correspond
to an integrated luminosity of 36 inverse picobarns. Comparisons are made
between the data and the predictions of different QCD-based Monte Carlo models
for multijet production. All models considered in this study are consistent
with the data for HT > 0.5 TeV. This measurement extends to an HT range that
has not been explored before.
