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?