a) 480
b) 510
c) 360
d) 377

Answer: c
Explanation:
$$\eqalign{ & {\text{Let the number of total workers}} = x \cr & {\text{Number of skilled workers}} \cr & = 75\% \,of\,x = \frac{{75x}}{{100}} = \frac{{3x}}{4} \cr & {\text{No}}{\text{. of unskilled workers}} \cr & = 25\% \,of\,x = \frac{{25x}}{{100}} = \frac{x}{4} \cr & {\text{No}}{\text{. of permanent workers}}, \cr & = {\frac{{80}}{{100}}} \times {\frac{{3x}}{4}} + {\frac{{20}}{{100}}} \times {\frac{x}{4}} \cr & = {\frac{{3x}}{5}} + {\frac{x}{{20}}} \cr & = \frac{{13x}}{{20}} \cr & {\text{No}}{\text{.}}\,{\text{of}}\,{\text{temporary}}\,{\text{workers}} = \cr & x – {\frac{{13x}}{{20}}} = \frac{{7x}}{{20}} \cr & \frac{{7x}}{{20}} = 126 \cr & x = 360 \cr} $$