Dario bakes a lasagna containing 2/3 pound of parmesan cheese, 1 1/4 pounds of ricotta cheese, and 1 1/3 pounds of mozzarella cheese. Dario cuts the lasagna into several equal slices, each containing exactly 1/4 pound of cheeses (of all types totaled). How many slices are there?

Parmesan                               Ricotta                               Mozzarella 

2/3                                            1 1/4                                         1 1/3


Get all the denominators to be the same

2/3 = 8/12, 1 1/4 = 5/4 = 15/12 , 1 1/3= 4/3 = 16/12   

Add them up:

39/12

Equation: 
39/12 / x = 1/4
         *x      *x
39/12 = 1/4 *x
       *4      *4
13=x

13 slices⇔