Question: There are 20 boys and 11 girls in the second grade and twice that number in the third grade. How many students are in grades 2 and 3?
Answer: Step-by-step reasoning process: There are 20 + 11 = 31 students in second grade. There are 31 x 2 = 62 students in third grade. In total, there are 31 + 62 = 93 students.
So the answer is 93.

Question: Robert had 25 balls. Tim gave him half of his 40 balls. How many balls does Robert have now?
Answer: Step-by-step reasoning process: Tim gave 40 / 2 = 20 balls to Robert. Robert now has 25 + 20 = 45 balls.
So the answer is 45.

Question: Nine members of the crafts club are making 2 necklaces each. It takes 50 beads to make each necklace. How many beads will they need in all?
Answer: Step-by-step reasoning process: Two bracelets need 50 x 2 = 100 beads. So they will need 9 x 100 = 900 beads in all.
So the answer is 900.

Question: 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?
Answer:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Step-by-step reasoning process: 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.
So the answer is 13000.