4.59 x 10-5 + 7.39 x 10-4

$${\mathtt{4.59}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{5}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{7.39}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{4}}} = {\mathtt{0.000\: \!784\: \!9}}$$

If you want to do some of it without a calc this is how

$$0.459\times 10^1\times 10^{-5}+4.39\times 10^{-4}\\\\
=0.459\times 10^{-4}+4.39\times 10^{-4}\\\\
=(0.459+4.39)\times 10^{-4}\\\\
=(0.459+4.39)\times 10^{-4}\\\\
= 4.849 \times 10^{-4}$$

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