A can do a piece of work in 16 days and B can do the same work in 20 days. In how many days can they do the same work, working together?

A can do (1)/(10) th of a piece of work in a day. B can do the same work in 15 days. In how many days can they do the same work, working together?

P can do a piece of work in 25 days and Q can do the same work in 15 days. In how many days they can complete the work by working together?

A can do (1)/(4) th of a piece of work in one day. While B can do (1)/(6) th of the work in a day. In how many days can they do the same work, working together?

A can do (1)/(4) th of a piece of work in one day. While B can do (1)/(6) th of the work in a day. In how many days can they do the same work, working together?