A dairy raised its daily milk collection from 8,000 litres to 9,400 litres in a year, while a neighbouring dairy went from 5,000 litres to 6,000 litres a day. Which dairy grew by the larger per cent, and by how much larger was that growth?

First dairy: the gain is 1,400 litres on 8,000, that is 1400/8000 = 17.5%. Second dairy: 1,000 litres on 5,000, that is 1000/5000 = 20%. The second grew faster, by 20 - 17.5 = 2.5 percentage points. The trap is to compare the absolute gains - the first dairy did add 400 litres more a day, but it built that on a far bigger starting figure, so its per cent growth is the smaller of the two.