Time and Work - General Questions

A is twice as efficient as B. Together they finish a job in 12 days. How long would A take to do it alone?

16 men can complete a work in 29 days. In how many days will 2 men complete the same work?

A can do a piece of work in 7 days and B can do it in 22 days. In how many days will they finish it working together?

A and B together can complete a work in 4 days. A alone can complete it in 8 days. In how many days can B alone complete the work?

30 men can complete a work in 34 days. In how many days will 10 men complete the same work?