The chef knows that 6 cooks can make 36 cakes in two hours. But, the chef needs 57 cakes. How many cooks does he need to make 57 cakes in one hour?

We need to find out 1) how many cakes does 1 cook make in two hours: 36:6=6; 2) how many cakes does one cook make in one hour: 6:2=3; 3) if the chef needs 57 cakes to be made in one hour, we can find out the number of cooks he needs that way: 57:3=19. So the chef needs 19 cooks to do this job.