  We consider a modified gravity theory, f(R)=R-a/R^n+bR^m, in the metric
formulation, which has been suggested to produce late time acceleration in the
Universe, whilst satisfying local fifth-force constraints. We investigate the
parameter range for this theory, considering the regimes of early and late-time
acceleration, Big Bang Nucleosynthesis and fifth-force constraints. We conclude
that it is difficult to find a unique range of parameters for consistency of
this theory.
