Question

篮球赛季前三场比赛中，乔伊丝前 $30$ 次投篮命中 $12$ 次，所以她的赛季投篮命中率是 $40\%$ 。在下一场比赛中，她投篮 $10$ 次，并把赛季命中率提高到 $50\%$ 。这 $10$ 次投篮中她命中了多少次？

Joyce made $12$ of her first $30$ shots in the first three games of the basketball season, so her seasonal shooting average was $40\%.$ In her next game, she took $10$ shots and raised her seasonal shooting average to $50\%.$ How many of these $10$ shots did she make?

$2$

$3$

$5$

$6$

$8$

答案：E

知识点：百分数平均数

难度评级：960

小提示：

下一场之后，她一共投篮 $30 + 10 = 40$ 次

After the next game she has attempted $30 + 10 = 40$ shots

大提示：

$40$ 次投篮的 $50\%$ 命中率表示总共命中 $20$ 次；她之前已有 $12$ 次

A $50\%$ average on $40$ shots means $20$ made in all; she already had $12$

解答：

第四场后她共投篮 $40$ 次。 $50\%$ 命中率表示她总共命中 $\tfrac12 \times 40 = 20$ 次。

她之前已经命中 $12$ 次，所以最后 $10$ 次中命中 $20 - 12 = 8$ 次。

所以正确答案是 E。

After the fourth game she has taken $40$ shots. A $50\%$ average means she made $\tfrac12 \times 40 = 20$ shots in total.

She had already made $12,$ so she made $20 - 12 = 8$ of the last $10.$

Thus, the correct answer is E .

1987 AMC 8 第 16 题

答案：E

难度评级：960

小提示：

大提示：

解答：

其他年份的第 16 题