Afsar, just remember that once you've done this, then as you add partitions to presumably achieve more than a single partition, then make sure you end up with a power of 2 number of partitions - or they will be skewed.
SQL> drop table t1 purge;
Table dropped.
SQL> drop table t2 purge;
Table dropped.
SQL>
SQL> create table t1 (
2 x integer
3 );
Table created.
SQL>
SQL> create table t2 (
2 x integer
3 ) partition by hash (x) (
4 partition p1
5 );
Table created.
SQL>
SQL> insert into t1 select rownum from dual connect by level <= 100000;
100000 rows created.
SQL> commit;
Commit complete.
SQL>
SQL> alter table t2 exchange partition p1 with table t1;
Table altered.
SQL>
SQL> alter table t2 add partition p2;
Table altered.
SQL>
SQL> exec dbms_stats.gather_table_stats('','T2')
PL/SQL procedure successfully completed.
SQL> select partition_name, num_rows
2 from user_tab_partitions
3 where table_name = 'T2';
PARTITION_NAME NUM_ROWS
-------------------- ----------
P1 50154
P2 49846
SQL>
SQL> alter table t2 add partition p3;
Table altered.
SQL>
SQL> exec dbms_stats.gather_table_stats('','T2')
PL/SQL procedure successfully completed.
SQL> select partition_name, num_rows
2 from user_tab_partitions
3 where table_name = 'T2';
PARTITION_NAME NUM_ROWS
-------------------- ----------
P1 24945
P2 49846
P3 25209
SQL>
SQL> alter table t2 add partition p4;
Table altered.
SQL>
SQL> exec dbms_stats.gather_table_stats('','T2')
PL/SQL procedure successfully completed.
SQL> select partition_name, num_rows
2 from user_tab_partitions
3 where table_name = 'T2';
PARTITION_NAME NUM_ROWS
-------------------- ----------
P1 24945
P2 24956
P3 25209
P4 24890
SQL>