请教几道数学题

yoo_hooUID: 137286

本人数学不好，请大家能够热心的帮助，谢谢各位！
  1. A rectangular tabletop consists of a piece of laminated wood
bordered by a thin metal strip along its four edges. The surface area of the tabletop is x square feet, and the total length of the strip before it was attached was x feet. If the tabletop is 3 feet wide, what is its approximate length, in feet ?
    (A) 12        (B) 10         (C) 9         (D) 8          (E) 6   
      答案是E，    我没读懂（阅读有点问题），更不知道该怎么做了 :(  

5 X4 H" T  i6 d6 e- |( x6 e  e: P  2.A student is asked to pick marbles from a bag that contains 18 marbles. Eight marbles are red, 4 are green, and 6 are black. What is the minimum number of marbles that a blindfolded student would have to draw from the bag to be certain of having at least three marbles of the same color?
- u  W4 s% n( y' ?1 P. C! o3 W答案是7，为什么啊，我觉的是5， 你看，三个都是同色的，那8个里面有2*3，4个里面有1*3，6个里面有2*3，  不是5吗？
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2 q$ Q* M9 o9 D* ~  3.A ranch has horses and ponies. Five-sixths of the ponies have horseshoes. Half of the ponies with horseshoes are Icelandic. If there are three more horses than ponies, what is the minimum number of horses and ponies on the ranch?
答案是27，  怎么求出来的呢？ 设，H+P=X， 5/6X=H，P=1/6X， 1/2*5/6X= 5/12X， 最小的话不应该是12吗？

0 G% a# o+ U7 ]/ T  4.A rectangular tiled floor consists of 70 square tiles. The rectangular floor is being rearranged so that 2 tiles will be removed from each row of tiles and 4 more rows of tiles will be added. After the change in layout, the floor will still have 70 tiles, and it will still be a rectangle. How many rows were in the tile floor before the change in layout?
9 A2 \3 |. u0 m% ?答案是10， 我设长的row=L ，短的row=W， LW=70， （L-2）（W+4）=70 = LW+4L-2W-8，方程最后多了个4L-2W=8， 下面该怎么做啊？

GITERUID: 138732

阅读看累了，偶来做做数学！~~呵呵
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2 t+ P' v/ p8 p4 V% G: i  N第一个你可以把它想成是两个rectangular,图就免了！现在你不知道的就是两个rectangular中间的那层东西有多厚，没关系，假设肯定>0好了！~然后可以有方程(3+x/3)X2>x！(左边是外面，右边是里面的面积，算出来(1/3)x肯定是小于6的！
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第二个没想明白你的星号是什么意思。反正就是运气最差的时候三个颜色每样拿了两个，然后最后又拿了一个，一共7个，你肯定是想偏了！

第三个，这个偶也看不出来前面的horse和后面的horseshoes有什么关系，就算没有好了！你中间列错了，12应该是the minimum number of ponies，然后12+15不就ok啦？

第四个，其实GRE数学不一定都是用方程解的，就算有方程也没有那么多未知数的，可以科学的估计一下！70=1X2X5X7，根据题目的要求，肯定是要拆成两个数相乘而且使他们的差最小，这样合适的只有是10X7和14X5，看看题目，前面的是remove&add之前的，后面的是之后的。不过这个题对行和列的表述都是row,所以大概7和10都可以吧！

继续做阅读...

sherry1225UID: 2192554

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