It's a finite series because it goes up by its own value. For example, it starts with 2 and then goes up 2 and then it gets to 4 and goes up 4 and etc.
For the pet the fraction is 2/3 because there is a fish,cat and a dog only cats and dogs have 4 legs and the fraction for the toy or the book is 1/2 because there are 2 objects and she can only get 1