Student 3 comes to class with probability 1.0 if both the others come and with probability 1/2

Question:

Student 3 comes to class with probability 1.0 if both the others come and with probability 1/2 if only one comes. Students 1 and 2 ignore each other.
A small class has only three students. Each comes to class with probability 0.9. Find the probability that all the students come to class and the probability that no students come to class in the above circumstances.