day 1

It is Saturday afternoon, and Cleve is spending it at his favorite place in the whole world: the pet shop. He is fascinated by the guppies, the puppies, and the frogs. He notices that the total number of guppies and frogs is 51. The total number of frogs and puppies is 17, and the total number of puppies and guppies is 58. How many guppies, how many puppies and how many frogs were in the pet store? (guppies: 46    puppies:12    frogs:5)

Solution: 
The total number of guppies, puppies and frogs is (51+58+17)/2=63
The number of guppies is 63-17=46
The number of puppies is 63-51=12
The number of frogs is 63-58=5