There are two groups A and B of a class, consisting of 42 and 28 students respectively. If the average weight of group A is 25 kg and that of group B is 40 kg, find the average weight of whole class?

[A]30 Kg

[B]31 Kg

[C]69 Kg

[D]70 Kg

**31 Kg**

Average weight of both groups =

Hence option [B] is correct answer.