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  4. The average weight of the students of a class is 60 kg. If eight new students of average weight 64 kg join the class, the average weight of the entire class becomes 62 kg. How many students were there in the class initially?

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Q. The average weight of the students of a class is $60 kg$. If eight new students of average weight $64 kg$ join the class, the average weight of the entire class becomes $62 kg$. How many students were there in the class initially?

Pair of Linear Equations in Two Variables

Solution:

Let there be $n$ students in the class. The total weight of the students after the eight new students join the class.
$60 n+64(8)=62(n+8) $
$\Rightarrow 60 n+64(8)=62 n+62(8) $
$\Rightarrow 62 n-60 n=64(8)-62(8) $
$\Rightarrow 2 n=8(2) \Rightarrow n=8$
$\therefore$ Initially, there were 8 students in the class.