conversations.from: human
conversations.value: Provide a step by step solution for the following math problem: On a construction site, the Laker cement factory provided 500 bags of cement sold to Mr. Zander at $10 per bag. Mr. Zander also received twenty lorries of construction sand, each carrying 10 tons of sand, sold at $40 per ton. How much money did Mr. Zander pay for these construction materials?
conversations.from: assistant
conversations.value: The total cost for the sand is 500*10 = $5000
  Since each lorry was carrying 10 tons of sand, the twenty lorries carried 20*10 = 200 tons.
  At $40 per ton, Mr. Zander paid 200*$40 = $8000 for the sand that was delivered to his construction site.
  Altogether, Mr. Zander paid $8000+$5000 = $13000 for the delivered construction materials.