  In this paper we show that a normal total number-of-particle fluctuation can
be obtained consistently from the static thermodynamic relation and dynamic
compressibility sum rule. In models using the broken U(1) gauge symmetry, in
order to keep the consistency between statics and dynamics, it is important to
identify the equilibrium state of the system with which the density response
function is calculated, so that the condensate particle number $N_0$, the
number of thermal depletion particles $\tilde{N}$, and the number of
non-condensate particles $N_{nc}$ can be unambiguously defined. We also show
that the chemical potential determined from the Hugenholtz-Pines theorem should
be consistent with that determined from the equilibrium equation of state. The
$N^{4/3}$ anomalous fluctuation of the number of non-condensate particles is an
intrinsic feature of the broken U(1) gauge symmetry. However, this anomalous
fluctuation does not imply the instability of the system. Using the random
phase approximation, which preserves the U(1) gauge symmetry, such an anomalous
fluctuation of the number of non-condensate particles is completely absent
