We estimate the number of quark jets in QCD multijet final states at hadron colliders. In the estimation, we develop the calculation of jet rates into that of quark jet rates. From the calculation, we estimate the improvement on the signal-to-background ratio for a signal semianalytically by applying quark-gluon discrimination, where the signal predicts many quark jets. We introduce a variable related to jet flavors in multijet final states and propose a data-driven method using the variable. As with the semianalytical result, the improvements in the signal-to-background ratio using the variable in Monte Carlo analysis are estimated.