A contractor was engaged to construct a road in 16 days. After working for 12 days with 20 labours it was found that only $${\frac{5}{8}}$$ th of the road had been constructed. To complete the work in stipulated time the number of extra labours required are ?

$$\eqalign{ & {\text{From, }} \cr & \frac{{{{\text{m}}_1} \times {{\text{d}}_1} \times {{\text{t}}_1}}}{{{{\text{w}}_1}}} = \frac{{{{\text{m}}_2} \times {{\text{d}}_2} \times {{\text{t}}_2}}}{{{{\text{w}}_2}}} \cr & {\text{Let extra workers be x}} \cr & \Rightarrow \frac{{20 \times 12}}{{\frac{5}{8}}} = \frac{{\left( {20 + x} \right) \times 4}}{{\frac{3}{8}}} \cr & \Rightarrow 4 \times 12 = \frac{{\left( {20 + x} \right) \times 4}}{3} \cr & \Rightarrow 36 = 20 + x \cr & \Rightarrow x = 16 \cr & \Rightarrow {\text{Extra workers }} = {\text{16}} \cr} $$