To find the width of Fiona's TV screen, we can use the Pythagorean theorem. The relationship between the length (L), width (W), and the diagonal (D) of a rectangle is given by:
\[ D^2 = L^2 + W^2 \]
where:
- \( D = 25 \) inches (diagonal)
- \( L = 20 \) inches (length)
- \( W \) is the width (which we want to find)
Plugging in the values we know:
\[ 25^2 = 20^2 + W^2 \]
Calculating the squares:
\[ 625 = 400 + W^2 \]
Now solve for \( W^2 \):
\[ W^2 = 625 - 400 \] \[ W^2 = 225 \]
Now take the square root to find \( W \):
\[ W = \sqrt{225} \] \[ W = 15 \]
Thus, the width of Fiona's TV is \( \text{15 inches} \).