Glibc package comes with a bundle of suits and all of them have the same version which glibc library has. ldd is one of the package that comes with glibc. Hence by checking the version of the ldd we can find the glibc version. Below is the command that is executed on linux rhel 6 64 bit environment and rhel 5.5 32 bit environment.
rhel6 64 bit
rhel 5.5 32 bit