urgent reply relating f9 required !

hey there, u said to post my querry here, n so am I. In f9 working cap management receivables early settlement discount topic, there is an interest saving on REDUCTION OF RECEIVABLES . the norm is to calculate fall in receivables i.e Current receivables with current days minus new receivables who takes discount plus who dont take discount . this net figure is the answer. like in WQZ question , current receivables 18000 minus (25% taking discount i.e $1800 plus 75% not taking discount i.e $10800 , total = $126000) so fall in receivables is $5400 !!!!!! same approach goes with Paislay Co question, KXP Co question,in all other questions and also in your Example 4 of working capital recevables . But in MARTON Co , they did’nt deduct new recevables (50% who takes up , 50% who dont take discount) with current recivables $4500. they just DIRECTLY COMPARED current recivables 4500 * 50% =2250 with 50% who take discount =438 thats it !!!!!!! (however the normal way should be they should add up 438 plus 2250 =2685 and deduct it by 4500 current receivables ! sir , Why this CONTRADICTORY method is used in MARTON? i am clear by the calculation, concept and arithematic , but MARTON is making me so confused ? plz resolve my issue THANKYOU