To find the total amount of flour used to make the bread, you need to add the initial amount of flour to the additional amount of flour added.
The initial amount of flour is \( \frac{4}{10} \) kg and the additional amount is \( \frac{3}{100} \) kg.
First, convert \( \frac{4}{10} \) to a fraction with a denominator of 100:
\[ \frac{4}{10} = \frac{4 \times 10}{10 \times 10} = \frac{40}{100} \]
Now add \( \frac{40}{100} \) kg and \( \frac{3}{100} \) kg:
\[ \frac{40}{100} + \frac{3}{100} = \frac{40 + 3}{100} = \frac{43}{100} \]
Thus, the total amount of flour used to make the bread is \( \frac{43}{100} \) kg.