种树

fzy · 发表于 2005-4-4 18:38:57

1. 10棵树种成5行，每行4棵，怎么种？ (Difficulty: +)

2. 11棵树种成6行，每行4棵，怎么种？ (Difficulty: ++)

3. 12棵树种成7行，每行4棵，怎么种？ (Difficulty: ++)

4. 13棵树种成9行，每行4棵，怎么种？ (Difficulty: +++)

新用户 · 发表于 2005-4-4 22:21:14

就是在五角星焦点处种树，5条线就是5行，每行4颗。

yma16 · 发表于 2005-4-4 22:56:19

a a a a
a a a a
a a a a
a a a

sean9991 · 发表于 2005-4-4 23:17:52

2 and 3

sean9991 · 发表于 2005-4-4 23:19:52

sean9991 · 发表于 2005-4-4 23:20:56

isn't that 15 trees?

怀疑 · 发表于 2005-4-5 02:20:13

I got an answer for No. 4

怀疑 · 发表于 2005-4-5 02:33:26

怀疑 · 发表于 2005-4-5 02:38:47

First draw four lines.

sean9991 · 发表于 2005-4-5 07:13:39

欢歌角度 · 发表于 2005-4-5 07:20:39

和前面的是一样的

fzy · 发表于 2005-4-5 18:30:26

The two answers for No. 4 (as well as my own answer) are structually the same. I solved it this way: Start with one line and two points on the line. Draw three other lines from each point. These six lines intersect and form a " 田字". Adjust the "田字" so that its two diagonals intersect the original line.

As far as I know, 9 is the best known result for 13 trees. The exact upper bound is still unknown, that is, no one proved it is not possible to have 10 rows, and no one did it either.

yma16 · 发表于 2005-4-6 00:29:07

回复：you are right.

fzy · 发表于 2005-4-6 19:29:56

Recently problem 4 appeared at WXC, with a ranking similar to the following:

6 rows : High School
7 rows : Bachelor
8 rows : Master
9 rows : Ph.D

Nice to see some Ph.D's here . There is only one Master and some Bachelors at WXC.

怀疑1 · 发表于 2005-4-6 21:35:17

I am also in WXC but did not see this problem

fzy · 发表于 2005-4-6 21:43:52

http://web.wenxuecity.com/BBSView.php?SubID=netiq&MsgID=30918

怀疑1 · 发表于 2005-4-6 22:36:41

You are right. I did not notice this problem. It seems that only two people at WXC tried, and these two guys are not among the best there.

fzy · 发表于 2005-4-6 23:42:13

I know. They probably didn't notice it either.

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种树

挑个简单的，我来回答第一题

回复：11棵树种成6行，每行4棵

2 and 3

answer for 2 and 3（图）

isn't that 15 trees?

I got an answer for No. 4

回复：I got an answer for No. 4（图）

回复：回复：I got an answer for No. 4（图）

answer for 4（图）

和前面的是一样的

Well done

回复：you are right.

ranking

I am also in WXC but did not see this problem

回复：I am also in WXC but did not see this problem

回复：回复：I am also in WXC but did not see this proble

I know. They probably didn't notice it either.