1. A small college requires its students to take at least one Mathematics course and at least one Science course. A survey of 140 of its students shows that: 60 completed their Mathematics requirement, 45 completed their Science requirement and 20 completed both Mathematics and Science requirements. Use a Venn diagram to find the number of students who had completed:
a. exactly one of the two requirements;
b. at least one of the requirements;
c. neither requirement.