A certain pet store has only cats and dogs. the ratio of the number of cats to the number of dogs in the pet store is 2:3. 1/4 of the cats and 1/2 of the dogs wear collars. if 48 animals wear collars, what is the total number of animals in the pet store?

The first thing we must do for this case is to define variables.
 We have then:
 x: number of cats
 y: number of dogs
 We write the system of equations:
 x / y = 2/3
 (1/4) x + (1/2) y = 48
 Solving the system we have:
 x = 48
 y = 72
 The total number of animals is:
 x + y = 48 + 72 = 120
 Answer:
 The total number of animals in the pet store is:
 120