If it takes 10 seconds for 10 printers to print out 10 pages of paper, how many seconds will it take 50 printers to print out 50 pages of paper?

We know that 10 printers print 10 pages of paper for 10 seconds.
In order to calculate how many seconds are needed for 50 printers to print out 50 pages  of paper -denoted with X, we should compare these situation with the situation we know (10 printers print 10 pages).
The number of printers is 5 times bigger and the number of pages is also 5 times bigger, which means we can write:
X=5*(seconds needed 10 printers to print 10 pages)
X=5*10seconds
X=50 seconds
It takes 50 seconds for 50 printers to print out 50 pages of paper.