Question

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 $48$ 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 $48$ free throws. How many free throws did she make at the first practice?

$3$

$6$

$9$

$12$

$15$

答案：A

知识点：等比数列逆推法

难度评级：900

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 $48$ ，前几次分别是 $24$ 、 $12$ 、 $6$ 、 $3$ 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 $48,$ the earlier practices had $24,$ $12,$ $6,$ and $3$ free throws.

Thus, the correct answer is A.

2004 AMC 12B 第 1 题

答案：A

难度评级：900

解答：

其他年份的第 1 题