  The coupled Gross-Pitaevskii equations for two-species BEC have been solved
analytically under the Thomas-Fermi approximation (TFA). Based on the
analytical solution, two formulae are derived to relate the particle numbers
$N_A$ and $N_B$ with the root mean square radii of the two kinds of atoms. Only
the case that both kinds of atoms have nonzero distribution at the center of an
isotropic trap is considered. In this case the TFA has been found to work
nicely. Thus, the two formulae are applicable and are useful for the evaluation
of $N_A$ and $N_B$.
