You have 562 gold fish and you need to have 18 in each tank, how many tanks do you need?
You first need to start with dividing the gold fish amount to the amount that can fit in each tank, (562 divided by 18 = 31.22222222222222). Then you multiply 18 by 31 and you get 558. This is obviously not as much goldfish as you had before, so to fix this you add another tank which makes 32 tanks, but you minus 562 from 558 and you have only 4 fish in the last tank.