AMC10 2011 A
AMC10 2011 A · Q6
AMC10 2011 A · Q6. It mainly tests Basic counting (rules of product/sum).
Set $A$ has 20 elements, and set $B$ has 15 elements. What is the smallest possible number of elements in $A \cup B$, the union of $A$ and $B$?
集合$A$有20个元素，集合$B$有15个元素。$A\cup B$（$A$和$B$的并集）的最小可能元素个数是多少？
(A)
5
5
(B)
15
15
(C)
20
20
(D)
35
35
(E)
300
300
Answer
Correct choice: (C)
正确答案：（C）
Solution
The union must contain all of the elements of $A$, so it has at least 20 elements. It is possible that $B$ is a subset of $A$, in which case there are no additional elements.
并集必须包含$A$的所有元素，因此至少有20个元素。$B$是$A$的子集是可能的，这种情况下没有额外的元素。
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