The average weight of some students in a class was 58.4 kg. When 5 students having the average weight 62.8 kg joined the class, the average weight of all students in the class increased by 0.55 kg. The number of students initially in the class, were:

The average weight of some students in a class = 58.4 kg

Let the total number of students be n.

Total weight of n students = 58.4n kg

The average weight of 5 students = 62.8 kg

Total weight of 5 students = 62.8 $$\times 5$$ = 314 kg

The average weight of (n + 5) students = 58.4 + 0.55 = 58.95 kg

Total weight of  (n + 5) students = 58.95(n + 5) kg

Total weight of n students + Total weight of 5 students = 58.95(n + 5)

58.4n + 314 = 58.95(n + 5)

58.4n + 314 = 58.95n + 294.75

0.55n = 19.25

n = 1925/55 = 35

$$\therefore$$ 35 students were initially in the class.