Finding the Third Proportional to 640.88 and 856.50

Step by Step Solution

1. Step 1: Write the proportion equation
   640.88 : 856.50 = 856.50 : x
2. Step 2: Convert to fraction form
   640.88/856.50 = 856.50/x
3. Step 3: Cross multiply
   640.88x = 856.50 × 856.50
4. Step 4: Simplify right side
   640.88x = 733,592.25
5. Step 5: Solve for x
   x = 733,592.25/640.88
6. Step 6: Final answer
   x = 1,144.67