12. The mean score of the students who took a mathematics test was 6 . Exactly $60 \%$ of the students passed the test. The mean score of the students who passed the test was 8 . What was the mean score of the students who failed the test?
A 1
B 2
C 3
D 4
E 5
12. C Let the mean score of the $40 \%$ of the students who failed the test be $x$. The information in the question tells us that $0.6 \times 8+0.4 \times x=6$. Hence $0.4 x=1.2$ and so $x=3$.