Separate the whole number from the decimal part. Convert the decimal part to a fraction and simplify.<br><br>
&bull; 3.4 = 3 + 0.4<br>
&bull; 0.4 = \( \frac{4}{10} \)<br>
&bull; Simplify: \( \frac{4 \div 2}{10 \div 2} = \frac{2}{5} \)<br>
&bull; 3.4 = 3\( \frac{2}{5} \)<br><br>
Final Answer: D: 3\( \frac{2}{5} \)