30 workers worked for 25 days and 35 workers worked for the remaining (37−25)=12 days. ∴ Total work =30×25+35×12. Now, if 5 extra men were not employed, then the time taken to complete the work. =
30×25+35×12
30
=25+7×2=39 days. He would have been lagging 39−38=1 day behind.