PL/SQL :: Grouping Records Based On Odd And Even Rows?

I have a sets of data in table ow_ship_det , from which i want to group all the records which are having same sl_desc but with the condition that sl_qty is not more than 1000 and sl_wt not more than 50000, i managed to do it but the problem is i want the wieght(sl_wt) and qty(sl_qty) to be evenly distributed among groups or boxes for example take the first four records which have common sl_desc 'H170' Where the qauntities are 15000,15000,10000,10000 as per the condition and loop written in program it will bring the 2 boxes or serial numbers with first 3 weights into 1 box as 40000 and other box as 10000, which i dont want instead i want to have them as 25000 each.

CREATE TABLE OW_SHIP_DET (SL_PM_CODE VARCHAR2(12),SL_DESC VARCHAR2(20), SL_WT NUMBER,SL_QTY NUMBER);
insert into ow_ship_det(sl_pm_code,sl_desc,sl_wt,sl_qty) values ('A','H170',15000,300);
insert into ow_ship_det(sl_pm_code,sl_desc,sl_wt,sl_qty) values ('B','H170',15000,300);
insert into ow_ship_det(sl_pm_code,sl_desc,sl_wt,sl_qty) values ('C','H170',10000,300);

[code]...

--if you see above the weight is not balanced properly in batches 0001 for H170 Desc it should get divided equally as below

ob_batch OB_PM_CODE OB_DESC OB_QTY OB_WT
0001                A           H170      300         15000
0001                C           H170       300        10000
0002                B           H170       300        15000
0002                D           H170       300        10000

[code]...