Kathleen had a bag of candy-coated chocolates. Of the 55 candies in the bag, 20% were red, 30% were orange, 30% were green, and 20% were blue. Of the blue ones, 20% had a damaged candy coating. Approximately how many of the blue ones had a damaged candy coating?
There were 55 x 0.20 = <<55*0.20=11>>11 red candies.
There were 55 x 0.30 = <<55*0.30=16.5>>16.5 orange candies (which we'll round up to 17).
There were 55 x 0.30 = <<55*0.30=16.5>>16.5 green candies (which we'll round down to 16).
There were 55 x 0.20 = <<55*0.20=11>>11 blue candies.
So, there were 11 x 0.20 = <<11*0.20=2.2>>2.2 blue candies that had a damaged candy coating.
Since we can't have a fraction of a candy, we'll round 2.2 up to 3.
Therefore, approximately 3 blue candies had a damaged candy coating. Answer: \boxed{3}.