求解道新东方绿皮数学题

hom0913UID: 3023725

1.In a certain apartment building exactly 1/3 of the apartments have two bedrooms and exactly 1/7 of  the two-bedroom apartment are front apartment. which of the following could be the total number of apartments in the building?
A. 42 B.50 C.51 D. 56 E 57

ps:  答案为A， 不知道怎么算的？ 特别是搞不懂 front apartment 是什么意思？

苏梳眠UID: 2717864

这个是个可能性的推断。
apartment building中有三分之一have two bedrooms。然后 two bedrooms的七分之一是 front apartment。
也就是说apartment building中有二十一分之一为 front apartment。
其中 front apartment肯定为整数，则apartment building必定为21的倍数。
答案为A。

hom0913UID: 3023725

非常感谢~·
分析的很到位！！