How much does a watch lose per day, if its hands coincide every 64 minutes?

At what time between 4 and 5 O' clock will the hands of a clock be at right angle?

At what time between 5 and 6 are the hands of a clock coincident?

At what time between 3 and 4 O' clock will the hands of a clock coincide?

Find at what time between 8 and 9 O' clock will the hands of a clock be in the same straight line but not together?

At what time between 9 and 10 O' clock will the hands of a watch be together?

Three pipes A,B and C attached to a cistern. A can fill it in 10 min, B in 15 min, C is a waste pipe for emptying it. After opening both the pipes A and B, a man leaves the cistern and returns when the cistern should have been just full. Finding, however, that the waste pipe had left open, he closes it and the cistern now gets filled in 2 min. In how much time the pipe C, if opened alone, empty the full cistern?

There is a group of 5 boys and 2 girls. The two groups working together can do four times as much work as a boy and a girl. Ratio of working capacities of a boy and a girl is: 

A group of 12 men can do a piece of work in 14 days and other group of 12 women can do the same work in 21 days. They begin together but 3 days before the completion of work, man's group leaves off. The total number of days to complete the work is: 

Vimal can do a piece of work in 20 days, Vimal and Kamal together can do in 12 days. If Kamal does the work only for half a day daily then in how many days the work will be completed ?