I'm pretty sure the math technically works out but bones are notoriously hard to buy at market value and bananas are notoriously hard to sell at market value. By 'notoriously' I basically mean that I tried it once to see if it was possible. I ended up losing money because I wasn't patient enough to buy/sell at market. So I guess probably technically it would make money, but you would need to buy a large amount in advance and be patient selling.