X can complete 5/7 part of a work in 10 days and Y can complete 3/4 part of the same work in 9 days. In how many days will both complete 13/21 part of the total work?

P can make a table in 16 days while Q can make it in 20 days. Q started the work and did that work for 5 days. In how many days P can complete the remaining work?

Type 1 workers are 2.5 times as efficient as type 2 workers. Twelve Type 1 workers can complete a task in 10 days. How many days would it have taken 4 Type 1 and 15 Type 2 workers to do the same work?

S does half as much work as T in 1/7 of the time taken by T. If together they take 21 days to complete a work, then how may days shall S take to complete that work alone?