上周我们给了一组袋鼠竞赛的题目（见《袋鼠数学竞赛题选（一）》），今天我们给出第二组题目，仍然是每个年级组各一题，并且对上一组题目进行解答。

1-2年级组

Place each of the numbers 1, 2, 3, 4, 5 into one box so that everything is correct. Which number goes into the box marked with question mark?

把数字1，2，3，4，5分别填入下图中的方框内，使得其中的算式都成立。标注问号的方框内应该填哪个数字？

3-4年级组

Josip has 4 toys - a car, a doll, a ball and a ship. He wants to put them on a line on a shelf. The ship has to be next to the car and the doll has to be next to the car. In how many ways can he arrange them so that all the conditions are fulfilled?

Josip有四个玩具：一辆车，一个洋娃娃，一个球和一只船。他想把这些玩具在架子上排成一排。船要跟车紧挨着，洋娃娃也要跟车紧挨着。他有多少种不同的方式排列这些玩具？

5-6年级组

On Jump Street, there are 9 houses in a row. At least one person lives in each house. Any two neighbouring houses together are inhabited by at most six people. What is the largest number of people that could be living on Jump Street?

有9栋房子依次座落在Jump街上。每栋房子里至少住了一个人，而且任意两栋相邻的房子里住的人数不超过6人。Jump街上最多住了多少人？

7-8年级组

A bush has 10 branches. Each branch has either 5 leaves only or 2 leaves and 1 flower. Which of the following could be the total number of leaves the bush has?

一丛灌木有10个分枝。每个分枝上要么有5片叶子，要么有2片叶子和1朵花。这丛灌木的叶子数量可能是多少？

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下面是上一组题目的参考答案和解析。

1-2年级组

The date 5/5/2015 has three 5's. The earliest date that will have three 5's again is:

在日期5/5/2015中，共出现了3个5。下一个出现了3个5的日期是：

【答案：E】所有答案的日期中都包含3个5，应选择其中最早的日期。

3-4年级组

In a speed skating competition 10 racers reached the final. Tom overtook 3 racers more than overtook him. Which place did Tom end up in?

在一次速滑比赛中，共有10个运动员到达了终点。在Tom后面冲线的人比在Tom前面的人多3人。Tom获得了第几名？

5-6年级组

Tom used 6 squares with side 1 to form the shape in the picture. What is the perimeter of the shape?

Tom用6个边长为1的正方形拼成了下图中的形状。这个图形的边长是多少？

7-8年级组

The diagram indicates the colours of some unit segments of a pattern. Luis wants to colour each remaining unit segment in the pattern either red or blue or green. Each triangle must have one side of every colour. What colour can he use for the segment marked x?

在下面的图案中，其中几条边的颜色已经标注出来了。Luis想把余下的边也涂成红、绿、蓝中的一种颜色，使得每个三角形的三条边刚好是不同的颜色。标注了字母x的边可以是什么颜色？

【答案：A】见下图，给不同的边进行编号。首先看编号为2的边，颜色不能是绿色，也不能是蓝色，所以只能是红色。进而推出编号为3的边颜色为蓝色。类似地，分别确定编号为6的边颜色为红色，编号为5的边颜色为绿色。最后，编号为4的边，颜色既不能跟边3同色，也不能跟边5同色，所以只能是红色。根据边3和边4的颜色，可知边x只能是绿色。