Question

萨莉投篮 $20$ 次后，命中率为 $55\%$ 。她又投 $5$ 次后，命中率提高到 $56\%$ 。最后 $5$ 次投篮中她命中了几次？

After Sally takes $20$ shots, she has made $55\%$ of her shots. After she takes $5$ more shots, she raises her percentage to $56\%.$ How many of the last $5$ shots did she make?

$1$

$2$

$3$

$4$

$5$

答案：C

知识点：百分数一次方程

难度评级：870

小提示：

先求萨莉前 $20$ 次命中了多少次

Find how many shots Sally had made after $20$ shots.

大提示：

再求她 $25$ 次投篮后的总命中数

Find how many total made shots she had after $25$ shots.

解答：

萨莉在最初的 $20$ 次投篮中命中了 $20 \times 0.55 = 11$ 次。于是 $\dfrac{11 + x}{25} = 0.56\text{，}$ 所以 $11 + x = 14$ 且 $x = 3$ 。

所以正确答案是 C。

Sally made $20 \times 0.55 = 11$ of her first $20$ shots. Then we get that $\dfrac{11 + x}{25} = 0.56,$ which tells us that $11 + x = 14$ and $x = 3.$

Thus, C is the correct answer.

2004 AMC 8 第 6 题

答案：C

难度评级：870

小提示：

大提示：

解答：

其他年份的第 6 题