How would you work this problem? a soda shop owner told his employee to add 2 1/5 cups of syrup to each gallon of soda. if there were 4 gallons of soda, how much syrup would be needed?

2 1/5 cups * 4 gallons =
2.2 cups * 4 gallons =
8.8 cups of syrup

This is a cross multiplication, proportion problem.  2 1/5 cups to 1 gallon as x cups are to 4 gallons.  You set it up like this:

2.2 cups/1 gallons= x cups/4 gallons
Cross multiply
(2.2*4)=(1*x)
8.8=x

So you need 8.8 cups for 4 gallons.  Since the question was asked in fraction form, your answer should also be in fraction form. 
8.8 = 8 8/10 = 8 4/5

So you need 8 4/5 cups for 4 gallons.

Hope this helps!  :)