Compute cost per completed task, wrong answers included

About this exercise

Tern Logistics wants the true cost of each model answering one shipment-status question. For each model, work out call_cost (input and output tokens at the listed prices), failure_cost (failure rate times the $0.60 a person costs to fix a wrong answer) and cost_per_task (call_cost plus failure_cost). Output one CSV code block with the header model,call_cost,failure_cost,cost_per_task and 3 rows in the order given, dollars as plain numbers with no $ sign. After the block, one line: "Cheapest per completed task: [model]".

Common mistakes when you ask AI for this

• Ignoring wrong answers. The AI computes only the cost of the call and picks Lark-S. Try: Say: "failure_cost = failure rate x $0.60, added to every task."
• Token-price slip. The AI mixes up per-million pricing and gets the call cost wrong. Try: Add: "Prices are per 1 million tokens: 2,000 tokens x $0.50 / 1,000,000."
• No clean CSV. The AI writes a markdown table or several code blocks. Try: Say: "One CSV code block with the header model,call_cost,failure_cost,cost_per_task."
• Prose around the data. The AI adds an explanation of every calculation. Try: Add: "After the block, only one line: Cheapest per completed task: [model]."

What a strong prompt includes

• Asks for a CSV block
• Gives the header
• Counts failures
• Uses the per-million pricing
• Limits the final line

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