Are we able to run SAP syst. for FI trans. only without inventory & costing modules the both modules will be run manually out of the system?

No, We need data to develop the report

Yes.If you have any other systems managing inventory and costing modules, it is technically possible to activate only Financial Accounting module in SAP without any influence from SAP-MM and SAP-PP/CO modules.

If  already a system   is already in  place fo  run inv.and cost

module fi module can be run   by sap. syst

I Agree With both Answers below, yes you can run, its techincally possible.

If you have any other systems managing inventory and costing modules, it is technically possible to activate only Financial Accounting module in SAP without any influence from SAP-MM and SAP-PP/CO modules.

But in the trend of cost cutting and benefit optimization scenarios, I do not see any relevance of having only SAP FI implemented even when the license cost is same to activate all these base functions within SAP.

Yes you can run the same. FI transactions if entered manually doesn't affect other logistics modules like MM and SD