Finding the Third Proportional to 640.72 and 871.38

Step by Step Solution

1. Step 1: Write the proportion equation
   640.72 : 871.38 = 871.38 : x
2. Step 2: Convert to fraction form
   640.72/871.38 = 871.38/x
3. Step 3: Cross multiply
   640.72x = 871.38 × 871.38
4. Step 4: Simplify right side
   640.72x = 759,308.01
5. Step 5: Solve for x
   x = 759,308.01/640.72
6. Step 6: Final answer
   x = 1,185.08