Suppose unharvested fruit is estimated at 80–110 kg. The seller reserves 15 kg and sells “the rest.”
The notional remainder might be 65–95 kg. The problem is not arithmetic alone; it is determining the unseparated subject of sale and deliverability.
If all fruit is first harvested and found to weigh exactly 90 kg, then 15 kg is put aside and the identified 75 kg sold, the transaction is factually different.