5 × 107 + 1.1 × 109 =
$${\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{107}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1.1}}{\mathtt{\,\times\,}}{\mathtt{109}} = {\frac{{\mathtt{6\,549}}}{{\mathtt{10}}}} = {\mathtt{654.9}}$$