There are 28 balls which are red, blue or green. If 12 balls are green and the sum of red balls and green balls is less than 24, at most how many red balls are there?  Options:
A) 10
B) 12
C) 11
D) 13
E) 14

Rationale: r + g + b = 28 g = 12 r + g < 24 = > r + 12 < 24 = > r < 12 = > at most 11 red balls answer : c
Answer: C