Some people finished the work in 40 days. But it will be completed in 30 days when joined 10 people. Find the number of people who were at the starting.
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Some people finished the work in 40 days. But it will be completed in 30 days when joined 10 people. Find the number of people who were at the starting.
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Solution :

 Let the no. of people at the beginning be $x$.

$\therefore$ From the question,

$$

\begin{aligned}

& 40 x=(x+10) \times 30 \\

\Rightarrow & 40 x=30 x+300 \\

\Rightarrow & 40 x-30 x=300 \\

\Rightarrow & 10 x=300 \\

\therefore & x=\frac{300}{10}=30 \text { people; Ans. }

\end{aligned}

$$

Trick : Required people

$$

\begin{array}{l}

=\frac{10 \times 30}{40-30} \\

=\frac{10 \times 30}{10}=30 ; \text { Ans. }

\end{array}

$$

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