Source: http://www.riddles-online.com/animal_riddles
......../canaries-and-cages-riddle-puzzle.htm

He puts one canary per cage, 
but has one bird too many. 

If he puts two canaries in each cage, 
he has one cage too many. 

How many cages and canaries does he have?

then the equations are
    B = C + 1
    and
    B = 2 C - 2

then
    C + 1 = 2 C - 2
    3 = C

So there are

4 Canaries and 3 Cages