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Are you sure the answer to second question is 12? I feel it should be 16: X * 2^-4 = 1 => x = 16. If 12 is the right answer, at the end of 10th minute, there would be 3 in the room and half of them leaving...
For question 3, we know the perimeter of the land by 3000/7.5=>400. If the length of sides are 5X and 3X. Then we have (5x+3x)*2 = 400 => x=25. Therefore we get 50 for the difference.
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