The average age of 39 students of a class is 39 years.

The average age of 39 students of a class is 39 years. If the age of the teacher is also included, the average age of the whole group becomes 40 years. The age (in years) of the teacher is:
एक कक्षा के 39 विद्यार्थियों की औसत आयु 39 वर्ष है। यदि शिक्षक की आयु को भी सम्मिलित कर ली जाए, तो संपूर्ण समूह की औसत आयु 40 वर्ष हो जाती है। शिक्षक की आयु (वर्षों में) ज्ञात कीजिए ?

81 77 79 83

Detailed Solution & Logic

Correct Answer:

79

Average age of 39 students= 39
Total age of 39 students = $ 39 \times 39 = 1521 $
New average with teacher = 40
Total persons = $ 39 + 1 = 40 $
Total age of group= $ 40 \times 40 = 1600 $
Teacher’s age = $ 1600 - 1521 = 79 $
Answer = 79 years

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