Two pipes A and B can fill a tank in 6 hours and 4 hours respectively. If they are opened on alternate hours and if pipe A is opened first, then the tank shall be filled in:
Five men and 2 boys can do as much work in 30 days as 7 men and 10 boys can do in 15 days. How many boys should join 40 men to do the same work in 4 days?
Working together, A, B and C can finish a piece of work in 3 hours. A finishes the same work in 8 hours and B finishes it in 6 hours. How long will it take for C alone to finish the same work?