The concept worked but not the implementation that i wanted.

Say when i execute the statement using "EXECUTE IMMEDIATE", i have to replace the variable ll_val1 & ll_val2 with the actual values, otherwise it prompts me with the following error

Declare
ll_val1 number(5) := 25;
ll_val2 number(5) := 50;
ll_formula varchar2(100) := 'll_val1 + ll_val2';
ll_result number(7) := 0;
begin
dbms_output.put_line('ll_val1 : ' || ll_val1 || ' , ll_val2 : ' || ll_val2 );
EXECUTE IMMEDIATE ('Select ' || ll_formula || ' From dual') INTO ll_result;
dbms_output.put_line(ll_result);
end;
/

ERROR at line 1:
ORA-00904: "LL_VAL1": invalid identifier
ORA-06512: at line 8

so, i had to change ll_formula := '25 + 50' to get the result.

So, as of now my problem is not solved.