【急】关于OG12里6.3节两道DS题的疑问与自己的看法

hengfengkobe · 发表于 2011-3-10 23:10:23

小弟在做OG12 6.3 Data Sufficiency Sample Questions时遇到了两道有争议的题（自认为的哈）as follows, 写下了自己的观点和疑问，希望各位大侠耐心看完，给个回复，3Q~

1、<原题> OG12 281页 102题
While on a straight road, Car X and Car Y are travelling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y?
(1)Car X is travelling at 50 miles per hour and Car Y is travelling at 40miles per hour.
(2)Three minutes ago Car X was 1/2 miles ahead of Car Y.

OG答案D 即1和2单独作为条件均sufficient. 但我认为还应考虑两车行驶方向，即分同向行驶和反向行驶两个情况考虑（题目条件中只给出两车匀速行驶，未注明方向）。1中给出了两车的速度，但在未注明方向时，从1mile 到2mile会有两个时间，反向行驶情况下，距离拉大所需时间更短。这样答案不唯一，1应为insufficient. 而2中，无论同向反向，在已知3min内差距拉大1/2mile的条件下，再拉大1mile所需时间均为6min(成比例) 所以我认为答案应为B

2、<原题> OG12 283页 122题‘
What is the volume of a certain rectangular solid?
（1）Two adjacent faces of the solid have area of 15 and 24, respectively
（2）Each of two opposite faces of the solid has area 40

OG答案C 但我理解“Each of two opposite faces”意思是任意两个对立面。而a rectangular solid 有6个面，3组对立面，那么2中each的意思是任意一组（两个）对立面面积都为40，那么两个面均为40，正方体。体积易得。不知道我的理解错在哪？请高人指点。

sdcar2010 · 发表于 2011-3-11 05:20:06

While on a straight road, Car X and Car Y are travelling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y?
(1)Car X is travelling at 50 miles per hour and Car Y is travelling at 40miles per hour.
(2)Three minutes ago Car X was 1/2 miles ahead of Car Y.

OG答案D 即1和2单独作为条件均sufficient. 但我认为还应考虑两车行驶方向，即分同向行驶和反向行驶两个情况考虑（题目条件中只给出两车匀速行驶，未注明方向）。1中给出了两车的速度，但在未注明方向时，从1mile 到2mile会有两个时间，反向行驶情况下，距离拉大所需时间更短。这样答案不唯一，1应为insufficient. 而2中，无论同向反向，在已知3min内差距拉大1/2mile的条件下，再拉大1mile所需时间均为6min(成比例) 所以我认为答案应为B

sdcar2010 · 发表于 2011-3-11 05:22:24

2、<原题> OG12 283页 122题‘
What is the volume of a certain rectangular solid?
（1）Two adjacent faces of the solid have area of 15 and 24, respectively
（2）Each of two opposite faces of the solid has area 40

OG答案C 但我理解“Each of two opposite faces”意思是任意两个对立面。而a rectangular solid 有6个面，3组对立面，那么2中each的意思是任意一组（两个）对立面面积都为40，那么两个面均为40，正方体。体积易得。不知道我的理解错在哪？请高人指点。

Only two faces have areas of 40. Plus having an area of 40 does not require the shape of a square (4*10, 5*8), etc.

When two conditions combined, the volume = (15*24*40)^(0.5) = 5*3*8=120.

【急】关于OG12里6.3节两道DS题的疑问与自己的看法

所属分类: GMAT考试

正在浏览此版块的会员 ()

浏览过的版块

【急】关于OG12里6.3节 两道DS题的疑问与自己的看法

所属分类: GMAT考试

正在浏览此版块的会员 ()

浏览过的版块

【急】关于OG12里6.3节两道DS题的疑问与自己的看法