In a youth camp, each participant must take part in at least one of the following activities: chess, backgammon or dominoes.
Of the total of 55 in the camp, 25 participants participated in chess,
24 in backgammon, and 30 in dominoes, 15 in both chess and
backgammon, 10 in both backgammon and dominoes, 5 in both
chess and dominoes, and 2 in all three events.

Find the number of participants who:
a) take part in one activity only
b) take part in exactly two activities
c) do not take part in at least two activities
d) take part in chess, given that they take part in dominoes
e) take part in backgammon, given that they do not take
part in dominoes.