If you run a race "twice as fast" as before that means you did it in half the time, right? If you run that race one third as fast it will take you three times as long. Note the inverse relationship - you divide the original time by the "times faster" factor. By this logic doing something in 25 seconds, and then doing it again 1.25 times faster means you did it in 25/1.25 = 20 seconds.