Answer:
256
Step-by-step explanation:The total amount os students is 1640 which is equivalent to 100% so we get 50% of 1640 which is equall to 820 students after that we also find 35% of 1640 which is equall to 564 students. After that we sum them up which we get 1384 students and subtract it from 1640 and get 256 students.