Question

Lincoln 中学八年级的 $39$ 名学生中，每人养一只狗、一只猫，或狗和猫都养。有二十名学生养狗， $26$ 名学生养猫。有多少名学生狗和猫都养？

Each of the $39$ students in the eighth grade at Lincoln Middle School has one dog or one cat or both a dog and a cat. Twenty students have a dog and $26$ students have a cat. How many students have both a dog and a cat?

$\ 7$

$\ 13$

$\ 19$

$\ 39$

$\ 46$

答案：A

知识点：容斥原理

难度评级：1000

解答：

同时养两种动物的人数等于养猫人数加养狗人数，再减去至少养一种动物的人数。

因此同时养两种动物的人数为 $20+26-39 = 7.$

所以正确答案是 A。

The number of people that have both animals is equal to the number of people that own a cat plus the number of people that own a dog minus the number of people that own either.

Therefore, the number of people who own both is $20+26-39 = 7.$

Thus, the answer is A .

2008 AMC 8 第 11 题

答案：A

难度评级：1000

解答：

其他年份的第 11 题