18 years is the average age of 36 boys and their professor. The average becomes 17 years if we leave the professor out. What is the age (in years) of the professor?

Correct option is A

​Given:

Average age of 36 boys and their professor = 18 years.

Average age of boys = 17 years.

Formula:

$$\text{Total Age} = \text{Average Age} \times \text{Number of People}$$​

Solution:

Total age of 36 boys and the professor: $$18 \times 37 = 666$$​​

Total age of 36 boys: $$17 \times 36 = 612$$​​

Age of professor: $$666 - 612 = 54$$ years