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:

A and B alone can complete a piece of work in 4 days and 8 days, respectively. In how many days will the work be completed, if they both work on alternate days starting with A?

If 4 men and 6 boys can do a work in 8 days and 6 men and 4 boys can do the same work in 7 days, then how many days will 5 men and 4 boys take to do the same work?

A is twice as good a workman as B and together they finish a piece of work in 13 days. In how many days will B alone finish the work?