Finding the Third Proportional to 428.50 and 641.88

Step by Step Solution

1. Step 1: Write the proportion equation
   428.50 : 641.88 = 641.88 : x
2. Step 2: Convert to fraction form
   428.50/641.88 = 641.88/x
3. Step 3: Cross multiply
   428.50x = 641.88 × 641.88
4. Step 4: Simplify right side
   428.50x = 412,003.52
5. Step 5: Solve for x
   x = 412,003.52/428.50
6. Step 6: Final answer
   x = 961.50