305 愈讀愈頭痛……

冇得返轉頭……，我應該要開始將成本嚴教授嘅 topology 啃左佢。(好彩佢個網有齊 homework 答案) 摺拉時數將創我自己新高，得閒記住探我。(睇黎又會好似 year 1 咁淨係顧 204 唔理其他科)

Some counting

Math 110 students are learning counting, now here is a suitable problem from HKgolden.

Problem. There are 2 guys, A and B, and there is a box containing 9000 balls numbered 1000, 1001, ..., 9999 respectively. Suppose A has chosen a ball with replacement, what is the probability that B chooses a ball with no digit in common with that of A? (Say if A has chosen 1234, then B will choose a number that does not contain any digit in {1, 2, 3, 4})

開學

期待嘅 fall sem 又開始喇，呢幾日叫做教得幾快 (以第一堂黎計) 嘅 course 可以叫 MATH321 及 MATH305。

(除非特別標明，以下所有 course code 均指 MATH)

星期三. 因為冇野做去 sit 下 217。全埸爆滿...，好多人 sit，原來 A 教授有一種規則，就係你喺佢個 first quiz 到 ``do well" 就可以去 reg 佢個 course (不需 al pure A 或 024 (或其他) 最少 A-)，難怪咁多人 sit 喇。不過聽講 203 一樣好多人 sit，啲學生未免太過份喇，搞到原本班學生冇位……。

今年 203 textbook 係用 rudin，呢屆真係好幸福，第一年就由 metric space 開始講起。有好有壞喇，以嚴教授果份 notes 黎教嘅話我最後學得好少 point-set topology on metric space (大部分相關知識都係李教授嘅 370 到學返黎的)，但相對地我開始接觸 305 嘅野 (204 的 multivariable differentiation 是煉獄的開始，linear algebra 不斷湧現...)。其實我懷疑 204 本身係 introduction to 305 (類似 202 係 introduction to 301)。

呢一日去到中午上 PHYS121，重點都係要知道交功課果個流程，其他都係一堆唔駛理嘅野...。

星期四. 如上一篇 entry 所見...，比較多堂嘅一日。321、305 李教授 (2號) 做左少少比較 deep 嘅 introduction。321 人真係好多...，305 反而好少人 sit (奇怪)。

305 第一堂李教授 (2號) 就恐嚇我地 ``Unlike MATH321, this is not a course for everyone, this course is for advanced student or student with strong background", ``This course is for student who wants to be a professional mathematician in the future" 云云。我諗...，呢啲說話只會令到學生鬥志更加激昂！

星期五. 冇乜特別，number theory...，有見識過出面嘅數學比賽都知道初等數論係非常困難...，論證雖然優美、簡單，但愈簡單嘅野對智力需求愈高 (追求初等證明是好習慣)，希望應付得黎。