If 100 poster printing machines printed 10,000 art posters in 100 days, how many days will take one machine to print one poster?

10,000 posters in 100 days, means 10,000/100 posters per day, that is 100/1 posters/day.

that simply means, the 100 machines print 100 posters in 1 day then.

now, if 100 machines, in 1 day they print 100 posters, that means 1 machine alone, is printing, the obvious :).