The GRAPES-3 extensive air shower consisting of a dense scintillator array and a 560 m square area tracking muon detector is designed to study the cosmic ray energy spectrum and composition over the knee region. Another muon telescope similar to the existing one is under construction and is expected to be operational within a year's time since the muon content is a sensitive parameter of the cosmic Ray primary composition, with the doubling of the area of the expanded muon detector, the mass separation of the different primary composition rays is expected to be improved at low energy when the muon density is low. Here we present our simulation studies of the sensitivity of the expanded muon telescope to the primary composition over 10-100 TeV. We used Corsika for shower simulation and GEANT-4 for simulating the detector response.