GAUSS8 2013 Problem 25

At the beginning of the winter, there were at least 66 students registered in a ski class. After the class started, eleven boys transferred into this class and thirteen girls transferred out. The ratio of boys to girls in the class was then 1:1. Which of the following is not a possible ratio of boys to girls before the transfers?

Answer Choices
A. 4:7
B. 1:2
C. 9:13
D. 5:11
E. 3:5