10 years ago the average age of all the 25 teachers of the Girls college was 45 years. 4 years ago, the principal has retired from her post at the age of 60 year. So after one year a new principal whose age was 54 years recruited from outside. The present average age of all the teachers is, if principal is also considered as a teacher:
Explanation:
10 years ago average age of 25 teachers = 45 years.
Average age of original 25 teachers (including the retired principal) = 45 + 10 = 55 years. ∴ Total age of original 25 teachers (including the retired principal) = 55 × 25 = 1375.
Present age of the retired principal = 60 + 4 = 64 years. Present age of the new principal = 54 + 3 = 57 years.
∴ Total age of new set of 25 teachers (excluding the retired principal but including the new principal) = 1375 – 64 + 57 = 1368.
∴ New average age of teachers = 136825 = 541825.
Hence, option (a).
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