David W. answered 03/09/16
Tutor
4.7
(90)
Experienced Prof
To change the units without changing the value, we use the Multiplicative Identity (that is, 1). We may multiply anything by 1 and it stays the same.
Let's call once around tract a "lap". That means that a lap = 1/8 mile. Or,
1 = (8 laps)/(1 mile) = (1 mile)/(8 laps) [we may choose the one to use]
So, Jon ran:
24 laps
(24 laps)*1
(24 laps) * ((1 mile)/(8 laps))
(24)*(1/8) miles [note: laps cancel out, leaving miles]
3 miles
Now, most teachers and tutors have done this so very many times that they forget how important the units are to someone who is learning. So, your son may see:
24/8 = 3
or 24*(1/8) = 3
or (1/8)*24 = 3
and then have to re-attach the units. It's better to get them correct from the start.
In words,
24 times around the track is 3 miles. (8 laps + 8 laps + 8 laps)