Finding the Third Proportional to 640.50 and 691.50

Step by Step Solution

1. Step 1: Write the proportion equation
   640.50 : 691.50 = 691.50 : x
2. Step 2: Convert to fraction form
   640.50/691.50 = 691.50/x
3. Step 3: Cross multiply
   640.50x = 691.50 × 691.50
4. Step 4: Simplify right side
   640.50x = 478,172.25
5. Step 5: Solve for x
   x = 478,172.25/640.50
6. Step 6: Final answer
   x = 746.56