If 80 Persons can finish a work in 16 days by working 6 hours a day, the number of hours a day should 64 persons work to finish that same job in 15 days is:

A can write 75 pages in 25 hrs. A and B together can write 135 pages in 27 hrs. In what time can B write 42 pages?

A can complete a piece of work in 10 days, B in 15 days and C in 20 days, A and C worked together for two days and then A was replaced by B. In how many days, altogether, work was completed?

Lal Babu and Mangallu can finish a work in 10 days while Lal Babu alone can finish that work in 15 days, then how many days will Mangallu take to do that work?

If A alone take 4 days more than A and B worked together. If B alone take 16 days more than A and B together. How many days they take together? 

Arun and Amit can do a piece of work in 9 days and 12 days respectively. If they work for alternate days and Amit starts the work first, then in how many days 35/36 parts of whole work will be completed?

A work is done by 30 workers not all of them have the same capacity to work. Every day exactly 2 workers, do the work with no pair of workers working together twice. Even after all possible pairs have worked once, all the workers together works for six more days to finish the work. Find the number of days in which all the workers together will finish the work?

If 28 men complete the $$ {7\over 8}$$ portion of a work in a week, then how many man will have to work to complete the remaining work in one finish.