To calculate \( 3.125 - 1.6 \), we can rewrite \( 1.6 \) as \( 1.600 \) to align the decimal places:
\[ \begin{array}{r} 3.125 \
- 1.600 \ \hline \end{array} \]
Now, subtract the numbers column by column:
- In the thousandths place: \( 5 - 0 = 5 \)
- In the hundredths place: \( 2 - 0 = 2 \)
- In the tenths place: \( 1 - 6 \) requires borrowing. We will borrow 1 from the units place, which makes the 3 a 2. So it becomes \( 11 - 6 = 5 \).
- In the units place: \( 2 - 1 = 1 \)
Putting it all together, we have:
\[ \begin{array}{r} 3.125 \
- 1.600 \ \hline 1.525 \ \end{array} \]
Thus, the answer is
\[ \boxed{1.525} \]