To find the thickness of a fingernail, we start with the diameter of a human hair and then add the thickness of the fingernail.
The diameter of a human hair is given as: \[ 4 \times 10^{-3} \text{ inches} \]
The fingernail is about \(0.011\) inches thicker than the hair. To find the thickness of the fingernail, we simply add the thickness to the diameter of the hair:
\[ \text{Thickness of fingernail} = \text{Diameter of hair} + 0.011 \]
Substituting the values: \[ \text{Thickness of fingernail} = 4 \times 10^{-3} + 0.011 \]
Now, let's convert \(0.011\) into decimal form:
- The decimal for \(0.011\) is easily manageable.
Converting \(4 \times 10^{-3}\) into decimal form: \[ 4 \times 10^{-3} = 0.004 \]
Now, we add these two values together: \[ 0.004 + 0.011 = 0.015 \]
Thus, the thickness of a fingernail, written as a decimal to three places, is: \[ \boxed{0.015} \]