Frodo drinks pints of milk a day. How much milk in cups does he drink? Write your answer as a whole number or a mixed number in simplest form. Include the correct unit in your answer.

One way to approach unit conversion problems is to match up the units in the conversion factor so they cancel.  To work the above problem we need a conversion factor to turn pints to cups.  That factor is 2 cups = 1 pint.  Written as a ratio this is

You can cancel units the same way you cancel terms when you multiply fractions.  Like units will cancel when one is on the bottom and one is on the top of the same or different fractions.

Now we have

Now the twos cancel leaving us with 7 cups.