Oh if only we had the rate in miles per second, mi/sec! Then we'd multiply that by the number of seconds and have the distance.
d = rt
Can we do this?
Yes, the rate 10 mph can be written as a fraction
10 mi/1 hr
recall you rules of multiplying fractions.
when the units in the top of one fraction match the units in the bottom of a fraction it's being multiplied by, those units drop out.
So let's get hr, which is in the denominator to drop out. I best put hr in the top of the next fraction then, right?
(10 mi/1hr)(1hr/60 min)
Now I want the min to drop out, so it best be in the next fractions numerator!:
(10mi/1 hr)(1 hr/60 min)(1 min/60 sec)
this is our rate in mi/sec
d = rt where t = 20 sec and r = 1mi/360sec
d = (1mi/360sec)(20sec)