Step-by-step explanation:
just think : what does 40 mph mean ?
it stands for
40 miles per hour
it means with that speed you will drive 40 miles in 1 hour.
20 miles in 1/2 hour.
80 miles in 2 hours and so on.
you always have to multiply both sides of the ratio with the same factor to keep the ratio itself unchanged.
so, as per the definition, it takes 1 hour to drive 40 miles when going 40 mph.
