katy left her house on a bicycle heading north at 8mph. At the same time her sister molly headed south at 12 mph. How long will it take for them to be 24 miles apart?

Hi again Amie;

Katie, 8 m/h North

Molly, 12 m/h South

They are traveling away from each other at a rate of (8+12) m/h.

distance=(rate)(time)

(distance)/(rate)=time

(24 miles)/(20 miles/hour)=time

Let's cancel miles located in both the denominator in numerator...

(24 miles)/(20 miles/hour)=time

Let's note the fact that the unit of hour is a denominator within the denominator. Henceforth, it is the numerator.

[(24)/(20)]hours=time

1.2 hours=time

Perhaps it would be better to express this in hours and minutes?

(1 hour)+(0.2 hours)=time

(1 hour)+[(0.2 hours)(60 minutes/1 hour)]=time

Let's cancel units where appropriate...

(1 hour)+[(0.2 hours)(60 minutes/1 hour)]=time

(1 hour)+(12 minutes)=time

NOW GET SOME SLEEP!