Each of four circles has a radius of 4 inches. A larger circle has an area equal to the total area of the four smaller circles. What is the length of the radius, in inches, of the larger circle?
If the length of the radius of a circle is multiplied by a factor of $k$, then the area of the circle is multiplied by a factor of $k^2$.  Since the larger circle has area 4 times greater than that of each smaller circle, the length of its radius is 2 times greater.  Therefore, the length of its radius is $2\times 4\text{ inches}=\boxed{8}$ inches.