选择题
2011 AMC 8 Problem 14: Girls at the Dance
There are 270 students at Colfax Middle School, where the ratio of boys to girls is 5:4. There are 180 students at Winthrop Middle School, where the ratio of boys to girls is 4:5. The two schools hold a dance and all students from both schools attend. What fraction of the students at the dance are girls?
A.
7/18
B.
7/15
C.
22/45
D.
1/2
E.
23/45