To find the thickness of a fingernail, we need to add the diameter of a human hair to the thickness difference provided.
The diameter of a human hair is approximately \( 4 \times 10^{-3} \) inches.
The thickness difference is given as 0.011 inches.
Now we add those two values together:
\[ \text{Thickness of fingernail} = \text{Diameter of hair} + \text{Thickness difference} \] \[ = 4 \times 10^{-3} \text{ inches} + 0.011 \text{ inches} \]
Converting \( 4 \times 10^{-3} \) to decimal form gives us:
\[ 4 \times 10^{-3} = 0.004 \text{ inches} \]
Now we can add the two values:
\[ 0.004 + 0.011 = 0.015 \text{ inches} \]
Therefore, the thickness of a fingernail is
\[ \boxed{0.015} \text{ inches} \]