Time and Work - General Questions

A is twice as efficient as B. Together they finish a job in 10 days. How long would A take to do it alone?

A is twice as efficient as B. Together they finish a job in 2 days. How long would A take to do it alone?

A is twice as efficient as B. Together they finish a job in 5 days. How long would A take to do it alone?

A and B together can complete a work in 6 days. A alone can complete it in 9 days. In how many days can B alone complete the work?

A can finish a work in 26 days and B in 26 days. They work together for 2 days and then A leaves. In how many more days will B finish the remaining work?