A butterfly that costs less than nothing
Three calls on the same stock, same expiry, equally spaced strikes: the -call at \15100$11110$6$.
Is there an arbitrage? Build the trade and state the convexity bound call prices must obey.
Show a hint
Buy the two outer strikes and sell two of the middle. Look at that package's payoff at expiry, and then at what it costs to put on today.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.