小学奥数题 高手请进

............设....................................................................................................正.........................方.....................................................形...........的边...........................................长...................................................为........................................................... S千..........................................米.....................................................................................................................
.............................................A......................................................................................................................................................................................................................N.....................比........N........................................B.............................=...........................................(2....................................................................................................................分....................................................之........................................................................................................................................................................................................S.......................-....................................N........................E...................)......................................÷....................(...............................2........................................分....................................之..........................S.............+..............................................................N......E.............................................)..............
1....................................2.........0分..........................................分.......之............S.......+...........6.......0......分之.......................................................................................................................................D..................P....................................................
1........................................................2...............0.....................................................分.....................................................................................................之...........................................S.....................................................................................+..........................6.................................................................................................................................................................0..............................分......................................................................................................................之2..........................P..................................................M..........................=8.....................................................+60..........分之（...................S-2............................................P.......................................................................................................................................................................................................................................................................................................................................................M.....................)........................................................................................................
...................................................分.................................................................................................................................................................................................................................................................................................................................之.......................................................5..........................................................................S......................................................................................
..........................................................................................................................................................................................................................................................................再.....................................................................................................................................................................................................................................................................................根...................................................................................................据........................................................................................................................................................同..............................................................一......................................时...............................................2...............分.................................之.......3）×......（......16分之......5S）=（（...........................32分.....................................................之........................）
................
..........................................................................................................................................................................................................................................................................................................................................................................................................................................................

首先要清楚 不管在什么点跑 相遇花费的时间肯定是一样的
所以PM指的是逆时针的车 少跑的路（因为第二次是从m点发车） 少花费的时间是PM/60 这部分时间 就是逆时针的车从第一次相遇点E开始跑到第二次相遇点N的时间
也就是说PM/60=NE/90

设正方形边长为a，DP为x，PC为a-x，
所以：a/2/90+a/80+x/60=（a-x）/60+a/120+a/2/90
x=（3/8）a
则以PC为中点，PM和MC都为（5/16）a
接着设AN为y，则BN为a-y 则列出方程为：
{（5/16）a+（3/8）a}/60+a/80+y/90=（5/16）a/60+a/120+（a-y）/90
解出y=a/32 则AN=a/32 BN=31a/32 所以AN:BN=1:31
思路：两次方程都抓住两车所用时间相等。

详解：设正方形边长为a，另设DP为x，则PC为a-x，则可以列出方程：a/2/90+a/80+x/60=（a-x）/60+a/120+a/2/90 解出x=（3/8）a
则以PC为中点，PM和MC都为（5/16）a
接着设AN为y，则BN为a-y 则列出方程为：
{（5/16）a+（3/8）a}/60+a/80+y/90=（5/16）a/60+a/120+（a-y）/90
解出y=a/32 则AN=a/32 BN=31a/32 所以AN:BN=1:31
思路：两次方程都抓住两车所用时间相等。
还有其他题目可以hi我！

先求DP和PC的比例：
设正方形边长为a,DP的长为x,则PC得长为a-x,根据他们的行驶时间相同可以列出如下方程，
x/60+a/80=(a-x)/60+a/120 x=3a/8 所以DP:PC=3:5
(3a/8)/60+a/80+AN/90=a/120+(a-AN)/90
再计算就可以得到答案了。