Q. 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?
Answer: 31 kg
Notes: Average weight of both groups = $latex = \frac{42\times25 + 28\times 40}{42+28}&s=1$ $latex = \frac{1050 + 1120}{70} = \frac{2170}{70} = 31 kg.&s=1$ Hence option [B] is correct answer.

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