Answer & Solution
Answer: Option B
Solution:
Let the required number of labourers be x
Less working hour/day, More labours (Indirect proportion)
More days, Less labourers (Indirect proportion)
\[\left. \begin{gathered}
{\text{Working hours/day 6}}:7 \hfill \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{Days 30}}:18 \hfill \\
\end{gathered} \right\}::30:x\]
$$\eqalign{
& \therefore 6 \times 30 \times x = 7 \times 18 \times 30 \cr
& \Leftrightarrow 6x = 126 \cr
& \Leftrightarrow x = 21 \cr} $$
