用十五秒可以将一根木料锯成4段,问：用同样的速度将这根木料锯成五段要几秒?注：要有单位,用分布,有答.一定要准确!

设火车的速度为x米/秒,根据题意：
15（x+1)=17（x-1)
解得 x=16（米/秒）
15(x+1)=255(米)
火车长255米.

90
因为画图就知道了,只需上6层!

后面的题目呢?是不是三人从同一点出发,多少时间再相遇.如果是这样
解题如下：一分钟要60秒,1分15秒是75秒,一分半是90秒
他们的最小公倍数是900秒,所以是12分后相遇

设这列火车速度为X千米/时
那么在甲身旁开过,用了十五秒,列火车长＝
（X+3.6）*（15/3600）
那么在乙身旁开过,用了十七秒,列火车长＝
（X-3.6）*（17/3600）
（X+3.6）*（15/3600）＝（X-3.6）*（17/3600）
X＝57.6千米/时
火车长＝（57.6+3.6）*（15/3600）*1000＝255米

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72°8′15″÷5
=70°÷5+2°8′15″÷5
=14°+（2×60′+8′15″）÷5
=14°+128′15″÷5
=14°+125′÷5+3′15″÷5
=14°+25′+（3×60′+15′）÷5
=14°+25′+195″÷5
=14°+25′+39″
=14°25′39″
还有什么地方不是很明白

15*(6-1)=75秒.

设车速为x km/h
(x+3.6)*15/3600=(x-3.6)*17/3600
解得x=57.6
则车长为方程一侧表达式的值
好像是255米

小明跑得快,他跑的时间短,速度快,小强跑的时间长,速度慢.这是常识逻辑题.

设身长x,速度y,则有(2x+300)/y=15…①
(2x+180)/y=12…②
求解方程组

（6-1）x15=75秒

The summer of Beijing in 2008 has witnessed one of the greatest Olympic Games the world has ever had in the past centuries since Modern Olympic Games was born in Athens Greece on April 6th,1896. Beijing has become the focus of the all the people around the world who love peace, friendliness, sports and the high spirits extracted from it. During the whole process of this big event, we have all enjoyed the wonderful performances of the athletes that came from all the countries of the world, which is a big success of this Olympic Games.
However, there is another success belonging to our Chinese, which is also one of the most attractive parts in 2008 Beijing Olympic in my eye. It is the volunteers, who came from every corner all over the country, from every university in Beijing, from every company or factory and cooperated with each other to guarantee the success of Beijing Olympic Games. The reasons why I think so will be presented as followed.
To begin with, it is the volunteers who have spared no effort to do their best to contribute to the success of this great Olympic Games. There would be no successful Olympic Games without the positive involvement of the excellent volunteers who were chosen from millions of voluntary people. There is no doubt that they had learned a lot of knowledge concerning the Olympic Games, the etiquette used in all kinds of situations, how to serve the people from all the countries around the world and so on. It is their considerate and detailed service that helped them get a 100-score test paper from the athletes, the Olympic Games Committee, as well as the people all over the world who came to visit Bejing in this specially wonderful Olympic Games.
Then,it is their hard voluntary work that fulfilled their commitment of "Smiling Beijing, Volunteering the Olympics and Co-creatinging the Harmony ". This is why I think the volunteers are the most lovely people besides the athletes in Beijing Olympic Games. The volunteers provided people that gathered in Beijing with the most humanistic service and help before, during and after the Olympic Games. Through the hard work of the volunteers, we convey to the whole world the friendliness of Chinese people and the longing dream we Chinese people have held in the past century. We finally proudly said that we did it!
Last but not least, the smiling faces of the volunteers became one of the impressive scene in 2008 Beijing Olympic Games. There is a saying that "the smile of the volunteers is the name card of Beijing", the core of which is to show the friendliness of Chinese people and how civilized we are, moreover, how great and powerful the country we are with the long history of 5000 years by showing the Confucius culture of harmony. Through the window of volunteers, the rest of the world came to know more about our great country and show more respect and admiration to our centuries-old culture essence.
In all, the volunteers have contributed a lot to 2008 Beijing Olympic Games which is indispensible to its big success. Although 2008 Beijing Olympic Games has successfully ended,let's learn from the volunteers their spirits of dedication and selflessness.Therefore, in my opinion, the volunteers are the most attractive part in 2008 Beijing Olympic Games.

这个问题的速度和时间分别是指什么?不看问题,就看题目的话,我能想到的问题是走路速度与跑步速度比.如果是两个速度比的话,下面是解题方法
设走路速度v,跑步速度w,算匀速的.回来时的跑步时间X,全路程S
可列方程：
5V+8w=S
10v+xw=s
10+x-（5+8）=3.25得x=6.25
x带入之后得10v+6.25w=s
即10v+6.25w=5V+8w 得v/w=7/20