hi
first thing to figure is the distance.
as distance = time *speed
with :
distance in km
time in = hour
an speed in = km/h
What do we have ? Speed is 80 km/h and is already in the good unit.
time is 45 minutes. But I need speed in hours and not in minutes, so
45 minutes is : 45/60 = 3*15 / 3*20 = 3*3*5 / 3*5*4 = 3/4 of an hour.
so distance is : 3/4 * 80 = 3 *4*20 / 4*1 = 3*20 /1 = 60
Distance is 60
Now if my speed is 120, and I have 60 km to do, as Time =
Distance/Speed we have = 60/120 = 0.5
note : the result is given in unit of time .Here the result say that we need an half unit of time to cover the distance.
As the unit we use is hours ( as speed is km/h ) so the math say : half an hour. Which is 30 minutes.
If speed were 150 km/h , the calculus would have been : 60/150 = 6/15 = 3*2 /5*3 = 2/5 of an hour.
and 2/5 of an hour composed of 60 minutes is :
2/5 * 60 = 2*60 / 5 = 2* 15*4 / 5 = 2*5*3*4 /5 = 24
24 minutes.
