Some Robertson-Walker models with variable G and Lambda

Some Robertson-Walker (RW) models admitting a contracted Ricci collineation along the fluid flow vector and having time-varying G and Lambda are investigated, The nature of the expansion of the models obtained in the cases k = +/- 1 is found to be interchanged from the corresponding standard FRW models. Estimates of the present values of various cosmological parameters are obtained and found to be well within the observational limits.