Question

In the above example, if the average weight is decreased by 1 $\mathrm{kg}$, then find the weight of new person.

Answer 1

 Let the average weight of a group $=x$

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

Let the weight of new person $=y$

$\therefore$ From the quetions,

$$

\begin{aligned}

& 30 x-40+y=30(x-1) \\

\Rightarrow & 30 x-40+y=30 x-30 \\

\Rightarrow & y=40-30 \\

\therefore & y=10 \mathrm{~kg} ; \text { Ans. }

\end{aligned}

$$

 

Trick : The age of new person $$ =40+30 $$ [New average - Old average] $$ =40+30 \times(-1)=10 \mathrm{~kg} ; \text { Ans. } $$