The average age of 24 boys and a teacher is 15. When the teacher's age is excluded, the average decreases by 1. What is the age of the teacher?

39 years

41 years

40 years

38 years

Total age of 24 boys and one teacher = 25 × 15 = 375 years

Average age of 24 boys = 15 − 1 = 14 years

Total age of 24 boys = 24 × 14 = 336 years

Teacher's age = 375 − 336 = 39 years