This is exercise 33 (p.158) from section 2.2 in Hatcher's Algebraic Topology:
Suppose the space $X$ is the union of open sets $A_1, \ldots, A_n$ such that each intersection $A_{i_1} \cap \cdots \cap A_{i_k}$ is either empty or has trivial reduced homology groups. Show that $\tilde{H_{i}}(X) = 0$ for $i \geq n-1$.
I'm pretty sure Mayer-Vietoris needs to be used, and that there should be some induction going on, but I haven't been able to figure it out.