Arbitrage Opportunity: Gelato

Gelaato (sic) in Barcelona sells 180g of gelato for €3.50 and 240g of gelato for €4.50 and.  So you can buy 2160g as either (a) 12 cups at €3.50 = €42; or (b) nine cups at €4.50 = €40.50.  I fully expect to see some 135-pound Wharton MBA in a black suit at the door arbitraging the €1.50 spread.