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 the whole class.
Options:
A . 70 kg
B . 30 kg
C . 31 kg
D . 69 kg
Answer: Option C Answer: (c)Required average weight= ${42×25+28×40}/{42+28}$= ${1050+1120}/70$ = $2170/70$ = 31kg Aliter : Using Rule 10, Here, $n_1$ = 42, $a_1$ = 25 $n_2$ = 28, $a_2$ = 40 ∴ Average = ${n_1a_1+ n_2a_2}/{n_1+ n_2}$
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