"A" can do a certain job in 4 hours, "B" can do the job in 6 hours, "C" can do the job in 8 hours. How long will it take to do the job if "A" and "B" work for 1 hour and "B" and "C" finish the job?
A tank can be filled by one pipe in 9 hours and another pipe in 12 hours. Starting empty, how...