  We prove that the obstruction bundle used to define the cup-product in
Chen-Ruan cohomology is determined by the so-called `age grading' or
`degree-shifting numbers'. Indeed, the obstruction bundle can be directly
computed using the age grading. We obtain a Kunneth Theorem for Chen-Ruan
cohomology as a direct consequence of an elementary property of the age
grading, and explain how several other results - including associativity of the
cup-product - can be proved in a similar way.
