prep求解。。。。

judyenglishS

what is the average height of the people in a certain group?
（1）the average height of the 3/n tallest people in the group is 6 feet 2.5 inches, and the average height of the rest of the people in the group is 5feet 10 inches.
（2）the sum of the heights of the n people is 178feet 9 inches.
答案选A 我觉得选D。。。。求真相。。。。

hangtianyuan

楼主题目都打错了。。。n/3
the average=(n/3 *a +2n/3  *b)/n=a/3+2b/3
A is sufficient

judyenglishS

太匆忙了。。。不好意思。。。为什么（2）不对呢。。。

fangzep

2不充分是因为n未知