Question 1176415
In a group of 120 students numbered 1 to 120,
 all even numbered students choose Physics,
120/2 = 60 students
 students whose numbers are divisible by 5 choose Chemistry and
120/5 = 24 students 
 those whose numbers are divisible by 7 choose Economics.
120/7 ~ 17 students
 How many students choose none of the three subjects?
120 - 60 - 24 - 17 = 19 students choose none of these