8.1 The average age of the teaching staff of a school, consisting of 20 teachers, was 49 years. When another teacher joined the school, the average age became 48 years. How old is the new teacher?
Answer: 28 years old. Solution: Before the new teacher arrived, the total age of the teachers was 49*20=980. Then the total age became 48*21=1008. Therefore, the new teacher is $1008-$ $980=28$ years old.