Amy K. answered • 04/29/17

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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.

Because

d = rt

Can we do this?

Yes, the rate 10 mph can be written as a fraction

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?

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)

10mi/3600sec

simplify to:

1mi/360 sec

this is our rate in mi/sec

d = rt where t = 20 sec and r = 1mi/360sec

d = (1mi/360sec)(20sec)

d=.055 mi