Which allocation validates the second formula with 100 original silver units and 49 silver units received?

Bab al-Sarf: Circulating Fulus, Obsolete Coins and Money-Changer Exchanges

• 100 for 49 silver, fulus unmatched
• 50 original silver for 49 silver
• 49 for 49 silver; remaining 51 against fulus
• Exclude the silver from possession rules