Explanation:
speed is always expressed as ratio
distance / time interval
so, his speed was
13.5/1.2 miles per hour (mph)
now we need to simplify this to x/1 mph or simply x mph.
in this ratio (which is a type of fraction)
13.5/1.2
the simplification needs to bring the denominator (bottom) to 1.
how can we transform 1.2 into 1 ?
by dividing it by 1.2.
and to keep the value of the overall fraction unchanged we need to do the same to the numerator (top).
so, we have
(13.5/1.2) / (1.2/1.2) = 11.25/1 = 11.25 mph