Average weight of 8 students is 45 kg. When a student is replaced by a teacher, then the average weight is increased by 4 kg. Calculate the weight of the teacher.

Total weight of 8 students = 8 × 45 = 360 kg. When one student is replaced by teacher, average becomes 49 kg (45 + 4). New total weight = 8 × 49 = 392 kg. Difference = 392 - 360 = 32 kg = teacher's weight - student's weight. Teacher's weight = 32 + student's weight. Without knowing the student's weight, teacher's exact weight cannot be determined.