jmc

Let the radius of the large circle be $R$. Then, the radius of the smaller circles are $\frac{R}{2}$. The areas of the circles are directly proportional to the square of the radii, so the ratio of the area of the small circle to the large one is $\frac{1}{4}$. This means the combined area of the 2 smaller circles is half of the larger circle, and therefore the shaded region is equal to the combined area of the 2 smaller circles, which is $\boxed{1}$.