The average age of 30 students is 9 years. If the age of their teacher is included, the average becomes 10 years. The age of the teacher, in years, is:
A
27
B
31
C
35
D
40
Correct Option:
D
Explanation
30 students × 9 years = 270 total years. With the teacher: 31 × 10 = 310. The teacher's age = 310 − 270 = 40 years.
