Three Days a Week

Difficulty: Medium · Topics: Discrete Mathematics, Sets, Word Problems

A music course that is open only on Fridays, Sundays and Tuesdays has 9 students, numbered consecutively 1, 2, 3, 4, …, 9.

- Everyone who comes to the course on Tuesday comes on Sunday as well. - The student who comes on Sunday but comes on neither Tuesday nor Friday has number 6. - The students who come on Sunday and Tuesday but not on Friday have numbers 1, 2 and 7.

How many students come to the course on Friday?