Since the whole set is composed of a total of 55 people, with 45 people being drinks of either coffer or tea, then the remaining people not included in the 45 would be the non-drinkers. So 55-45, meaning there are 10 people who drink neither tea nor coffee. To obtain the probability:
10/55 = 2/11 = 0.182
Therefore, the probability of a person being picked at random does not drink either coffee or tea is 0.182.