[不恥下問系列]又有GMAT數學題不懂之3

From a bag containing 12 identical blue balls, y identical yellow balls, and no other balls, one ball will be removed at random. If the probability is less than 2/5 that the removed ball will be blue, what is the least number of yellow balls that must be in the bag?
1) 17
2) 18
c) 19
D) 20
E)21

THX!!!!