12 typists working for 4 hours per day to type a book in 18 days. How many days will 4 typists have to work for 8 hours per day to type the same book?
Twelve typists, all working with same speed, type a certain number of pages in 18 days working 8 hours a day. Find, how many hours per day must sixteen typists work in order to type the same number of pages in 9 days?