# Sub branching fraction calculation

I am puzzled with the branching fraction calculation in the case of multiple decays. Let I have this decay $$B(X \rightarrow a + b) = 0.5$$. Now I know the $$B(a\rightarrow c)=0.1$$. Now can I say the $$B(X \rightarrow a(\rightarrow c) + b) =0.5*0.1 =0.005?$$. Or is it possible to get $$B(X \rightarrow a(\rightarrow c) + b)$$ with only this information?

Thanks