2004 AMC 12B 第 1 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
1.
上周每次篮球训练时，Jenny 罚中的球数都是前一次训练罚中球数的两倍。她第五次训练罚中 球。她第一次训练罚中了多少球？
At each basketball practice last week, Jenny made twice as many free throws as she made at the previous practice. At her fifth practice she made free throws. How many free throws did she make at the first practice?
小提示：
往前推时，每次训练罚中的球数都是下一次的一半。
Each practice she made half as many as the next practice
大提示：
把 连续四次除以二，就能回到第一次训练
Halve four times to reach the first practice
解答：
每次训练罚中球数都是前一次的两倍，所以倒着推要除以二。第五次是 ，前几次分别是 、、、 球。
因此正确答案是 A。
Each practice she made twice the previous, so going backward we halve. From the fifth practice at the earlier practices had and free throws.
Thus, the correct answer is A.
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