Geometry

Question Analysis

The main focus is using the area formula for a ring to solve for the unknown inner radius, given the area of the ring and the outer radius.

Key Concept Explanation

The area formula for a ring is , where  is the area of the ring,  is the outer radius, and  is the inner radius. This formula is derived from subtracting the area of the inner circle () from the area of the outer circle ().

Step - by - Step Solution

1. Start with the area formula for a ring: .

Given that   and  in, substitute these values into the formula: