Rekha and Sonali received Rs.2800 as wages for 20 days for the work they did together. Rekha’s efficiency in the work was three times that of the Sonali. What are the daily wages of Sonali?
Two pipes can fill a tank in 15 hours and 4 hours, respectively, while a third pipe can empty it in 12 hours. How long (in hours) will it take to fill the empty tank if all the three pipes are opened simultaneously?