请问机经78题怎么做?

jessieflybir · 发表于 2010-11-13 20:47:45

一个立方体，外面painted成red的。边长6里面，现在切开来，切成216个小正方体（就是边长1厘米了），问没红色油漆的有几个？虽然有答案,可是还是不明白.请教高人指点.

lpilikeit · 发表于 2010-11-13 21:53:34

表面涂成红色后，切割出的小正方体中，那些有一面曾是大正方体表面的，就会在表面有红色，把大正方体的个各面都除掉1cm（除掉的这1cm都是有面带红色的小正方体），表面完全没有红色的就是最中心的、没有面曾是大正方体面的那些，也就是除掉1cm后剩下的正方体的体积=4×4×4=64

sdcar2010 · 发表于 2010-11-13 23:10:20

You just need to count how many tiny cubes (1x1x1) have a surface or surfaces which are part of the surface of the bigger cube.

The volume of the bigger cube is 6^3 = 216. This is also the total of the small tubes

Now imagine that you cut off the outside cubes which have paint on, what do you get? Since each face has to be "peeled of" by 1, you get a new cube with the edge at 4. The total volume of this new tube is 4^3 = 64, which is also the number of tubes that have NO paint on any of its surfaces.

What is the number of tiny tubes being cut off? 216 - 64 = 152 Then 152 would be the number of tubes who have its face or faces painted.

一眼万年 · 发表于 2010-11-13 23:12:49

LS同学还是不要用英文来回答JJ题吧！！！！！！！

sdcar2010 · 发表于 2010-11-13 23:42:20

Aren't we living in a free country?

一眼万年 · 发表于 2010-11-14 00:32:38

哈哈，有劲的！

请问机经78题怎么做?

所属分类: GMAT考试

正在浏览此版块的会员 ()

浏览过的版块