AMC10 2010 B
AMC10 2010 B · Q3
AMC10 2010 B · Q3. It mainly tests Pigeonhole principle.
A drawer contains red, green, blue and white socks with at least 2 of each color. What is the minimum number of socks that must be pulled from the drawer to guarantee a matching pair?
抽屉中有红、绿、蓝、白四种颜色的袜子，每种颜色至少有 2 双。要保证抽出一双同色袜子，至少需要抽出多少双袜子？
(A)
3
3
(B)
4
4
(C)
5
5
(D)
8
8
(E)
9
9
Answer
Correct choice: (C)
正确答案：（C）
Solution
If a set of 4 socks does not contain a pair, there must be one of each color. The fifth sock must match one of the others and guarantee a matching pair.
如果抽出的 4 双袜子没有同色对，则每种颜色各一双。第五双袜子必然与其中一双匹配，从而保证有一双同色袜子。
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