If an inlet pipe fills a tank in 10 hrs and another inlet pipe fills the same tank in 5 hrs then time required to fill the tank when both pipes are opened.

An inlet pipe can fill a tank in 10 hrs and an outlet pipe empties the same full tank in 20 hrs. The time required to fill the tank when both pipes are opened.

Alia can complete an assignment in 5 days and Babar can complete the same assignment is 20 days. The time taken by both Alia and Babar to complete the assignment working together is