2. 外语
  3. In a list of numbers, the first number is 3, the second is 4, and each subsequent number is the sum of all the preceding numbers

In a list of numbers, the first number is 3, the second is 4, and each subsequent number is the sum of all the preceding numbers

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问题 In a list of numbers, the first number is 3, the second is 4, and each subsequent number is the sum of all the preceding numbers in the list. If the 20th number in the list is x, what is the 25th number in the list?
选项 A、7x
B、16x
C、32x
D、35x
E、161x
答案C
解析 在一个数列中，首项为3，第二项为4，并且下一项是前面所有项的和。若该数列中第20项是x，问第25项是多少?
解：本题的正确答案为(C)。第20项为x，则前19项的和也是x，第21项为2x，22项为4x，由此可推出第25项是32x。
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