## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$3$
Using the diagram: $n(\text{students in at least one course})=4+9+2+7+22+8+15=67$ (These are the numbers inside the circle that represents at least one of the courses.) The total number of students is $70$. Thus, the number of students not taking any course is: $70-67=3$.