Finding the Third Proportional to 399.09 and 399.09

Step by Step Solution

1. Step 1: Write the proportion equation
   399.09 : 399.09 = 399.09 : x
2. Step 2: Convert to fraction form
   399.09/399.09 = 399.09/x
3. Step 3: Cross multiply
   399.09x = 399.09 × 399.09
4. Step 4: Simplify right side
   399.09x = 159,275.82
5. Step 5: Solve for x
   x = 159,275.82/399.09
6. Step 6: Final answer
   x = 399.09