The average age of 24 students in a class is 15 years. When the teacher's age is included, the average increases by 1. What is the teacher's age (in years)?

50 45 55 40

40

Total age of 24 students = 24 × 15 = 360 years Total age of 24 students & 1 teacher = ( 24 + 1 ) × 16 = 25 × 16 = 400 years Age of teacher = 400 - 360 = 40 years