Finding the Third Proportional to 309,640.50 and 678,289.50

Step by Step Solution

1. Step 1: Write the proportion equation
   309,640.50 : 678,289.50 = 678,289.50 : x
2. Step 2: Convert to fraction form
   309,640.50/678,289.50 = 678,289.50/x
3. Step 3: Cross multiply
   309,640.50x = 678,289.50 × 678,289.50
4. Step 4: Simplify right side
   309,640.50x = 460,076,645,810.25
5. Step 5: Solve for x
   x = 460,076,645,810.25/309,640.50
6. Step 6: Final answer
   x = 1,485,841.31