Finding the Third Proportional to 428.50 and 642.50

Step by Step Solution

1. Step 1: Write the proportion equation
   428.50 : 642.50 = 642.50 : x
2. Step 2: Convert to fraction form
   428.50/642.50 = 642.50/x
3. Step 3: Cross multiply
   428.50x = 642.50 × 642.50
4. Step 4: Simplify right side
   428.50x = 412,806.25
5. Step 5: Solve for x
   x = 412,806.25/428.50
6. Step 6: Final answer
   x = 963.38