Time and Work Questions

In a computer game, there are builders and destroyers. Together there are 20 of them. Some of them try to build a wall around a castle while the rest try to demolish it. Each of the builders can build the wall alone in 15 hours while any of the destroyers can demolish it in 10 hours. If all 20 builders and destroyers are made active when there is no wall and the wall gets built in 3 hours, how many of them are destroyers?

Surya works 3 times as fast as Ramya and is able to complete a work in 40 days less than the number of days taken by Ramya. Find the time in which they can complete the work together.

A can complete a task alone in 8 days, while B takes 12 days to do it by herself. Together with C it takes them 4 days to complete the work. If C and D together can complete the task in 15 days, then how many days will D need to complete the task by herself?

Both A and B together can complete a work in 20 days and B alone can complete the same work in 36 days. In how many days will A alone complete the work?

A and B can complete a task in 12 days. However, A had to leave a few days before the task was completed and hence it took 16 days in all to complete the task. If A alone could complete the work in 21 days, how many days before the work getting over did A leave?

Vikram and Vivek can finish a work in 50 days. They worked together for 20 days and then left. How much work has been done by them?

9 women can complete a work in 50 days. If more 6 women were added to them, how many days before the work can be completed?

In a camp 180 students had ration for 20 days. How many students should leave the camp if the ration should last for 25 days?