Finding the Third Proportional to 640.72 and 1,396.78

Step by Step Solution

1. Step 1: Write the proportion equation
   640.72 : 1,396.78 = 1,396.78 : x
2. Step 2: Convert to fraction form
   640.72/1,396.78 = 1,396.78/x
3. Step 3: Cross multiply
   640.72x = 1,396.78 × 1,396.78
4. Step 4: Simplify right side
   640.72x = 1,950,981.49
5. Step 5: Solve for x
   x = 1,950,981.49/640.72
6. Step 6: Final answer
   x = 3,044.97