OG 12 3.1 Diagnostic Test--Quantitative Sample questions--No.34

zwednesday

各位...恕我愚钝...这题实在不明白什么...求指点啊...
of the companies surveyed abt the skills they required inprospective employees, 20 % required both computer and writing skills. What % of computer surveyed required neither computer skills nor writing skills?
1)of those companies surveyed that required computer skills, half required writing skills.
答案推出来categore 1 = category2, 为什么?

sdcar2010

100 companies. 20 require both computer and writing skills. X require computer skill only. Y require writing skill only. Z require NONE skill. So X+Y+Z = 80. And the question ask for Z

1) X=20 since among the companies requiring computer skills, half require writing skills. Since Y is unknown, insufficient.