The efficiency of A, B, and C is 2 : 3 : 5. A alone can complete a work in 50 days. They all work together for 5 days and then C left the work, in how many days A and B together can complete the remaining work?
A boat covers 12 km upstream & 18 km downstream in 3 hrs, while it covers 36 km upstream & 24 km downstream in 6.5 hrs. What is the speed of the current?