Imagine a question and stream-of-consciousness explanation for which this is the answer: 250

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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Question: The moon is made of 50% iron, 20% carbon, and the remainder is other elements. Mars weighs twice as much as the moon, but has the exact same composition. If Mars is 150 tons of other elements, how many tons does the moon weigh?
Stream-of-consciousness: 30% of Mars is made up of other elements because 100 - 50 - 20 = 30. Mars weighs 500 tons because 150 / .3 = 500. The moon weighs 250 tons because 500 / 2 = 250.