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If a person whose average weight is $40 \mathrm{~kg}$ is replaced from a group of 30 persons and a new person comes, then the average weight is increased by $1 \mathrm{~kg}$. Find the weight of new person.

Solution-

: Let the average wt. $=x$

$\therefore$ Total weight of 30 persons $=30 x$

The weight of new person $=y$

$$\begin{array}{l} \therefore 30 x-40+y=30(x+1) \\ \Rightarrow 30 x-40+y=30 x+30 \end{array}$$

$\therefore y= 70 kg$

Trick :

Required weight $=40+30 \times 1$

$=70 \mathrm{~kg}$; Ans.

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