2022-1-4

还有一天就要开学了。把1985年美国初中数学竞赛（American Junior High School Mathematics Examination）的试题，让小不点儿给打印出来，然后我和她一起做，限时40分钟，看谁先做完，谁对的更多。

这些看起来比较容易的题目，竟然两个人都在规定的40分钟内，没法做完，每人都瞎猜了叁道题，剩下的22道题，小不点儿错了叁道，我错了两道。瞎猜的叁道题中，小不点儿对了一道，我叁题全错。

结果是打成了平手，每人答对20题，错五题。其中小不点儿猜对的那一道题的解题思路，竟然在标准答桉当中。

第25题：Five cards are lying on a table as shown.

Each card has a letter on one side and a whole number on the other side. Jane said, If a vowel is on one side of any card, then an even number is on the other side. Mary showed Jane was wrong by turning over one card. Which card did Mary turn over? (Each card number is the one with the number on it. For example card 4 is the one with 4 on it, not the fourth card from the left/right).

小不点儿解答策略很微妙，找那个与众不同的：Using the answer choices, we see that P and Q are logically equivalent (both are non-vowel letters) and so are 4 and 6 (both are even numbers). Thus, if one of these is correct, then the other option in its pair must also be correct. The only remaining answer choice is 3.

关键是，我不小心做错的那两道题，小不点儿都给做对了。

孺子，可教也！

小不点儿最不应该做错的一道题，是一道填数字的题：

多做一次类似的练习，就可以迎刃而解了。