[問題]GWD-17 Q2

[MMK]

A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of of distinct letters written in alphabetic order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?
A. 4
B. 5
C. 6
D. 7
E. 8

Answer: B

看來放了一個年假我的頭腦也跟著放假了
感覺好像蠻基本的題目哩 可是就轉不過來
煩請大家幫忙解答好嗎?

我是這裡新加入的成員，所以如果我的提問有什麼不夠周到的地方，
請大家指正我喲^^謝謝大家，一起加油喔~

[lioyd]

A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of of distinct letters written in alphabetic order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?
A. 4
B. 5
C. 6
D. 7
E. 8

Answer: B

看來放了一個年假我的頭腦也跟著放假了
感覺好像蠻基本的題目哩 可是就轉不過來
煩請大家幫忙解答好嗎?

我是這裡新加入的成員，所以如果我的提問有什麼不夠周到的地方，
請大家指正我喲^^謝謝大家，一起加油喔~

妳可以先假設三個字母的情況：ABC
a single letter的清況： A、B、C=>3 個，
a pair of of distinct letters written in alphabetic order的清況：AB、AC =>2個；BC =>1個

∴從上面可以找到規律：3 個字母共有(3+2+1)種編碼；4個字母共有(4+3+2+1)種編碼(妳可以自己test一下)
∴若有5個字母，共有5+4+3+2+1=15>12 (四個字母只有4+3+2+1=10<12，不符)

[MMK]

嗯嗯^^懂了
感謝lioyd大大 喔:laugh~~~~~~