The average monthly salary of 660 workers in a factory is Rs. 380. The average monthly salary of officers is Rs. 2100 and the average monthly salary of the other workers is Rs. 340. Find the number of other workers.

$$\eqalign{ & {\text{Total}}\,{\text{salary}}\,{\text{of}}\,660\,{\text{workers}} \cr & = 660 \times 380 \cr & = Rs.\,250800 \cr & {\text{If}}\,{\text{other}}\,{\text{workers}}\,{\text{be}}\,x;\,{\text{then}}, \cr & = \left + 340x \cr & = 250800 \cr & Or,\,1386000 - 2100x + 340x = 250800 \cr & 1760x = 1135200 \cr & {\text{Hence}},\,x = \frac{{1135200}}{{1760}} = 645 \cr & {\text{Number}}\,{\text{of}}\,{\text{other}}\,{\text{workers}} = 645 \cr} $$