The average weight of 30 students in a class is 25 kgs. If the weight of the class teacher is added, the average weight increase by 2 kgs. The weight of the class teacher (in kgs) is:

The definition of average (arithmetic mean) is:

average weight $$=$$ total weight $$\div$$ number of persons

Initially, only the 30 students are considered.

Total weight of 30 students $$=$$ number of students $$\times$$ their average weight
$$=30 \times 25=750\text{ kg}$$

After including the class teacher, the number of persons becomes
$$30+1 = 31$$

The average weight now rises by $$2\text{ kg}$$, so the new average weight is
$$25 + 2 = 27\text{ kg}$$

Total weight of the 31 persons $$=$$ number of persons $$\times$$ new average weight
$$=31 \times 27 = 837\text{ kg}$$

Weight of the class teacher $$=$$ total weight of 31 persons $$-$$ total weight of 30 students
$$=837 - 750 = 87\text{ kg}$$

Therefore, the class teacher weighs $$87\text{ kg}$$.

Option D which is: 87