Finding the Third Proportional to 309,708 and 678,432

Step by Step Solution

1. Step 1: Write the proportion equation
   309,708 : 678,432 = 678,432 : x
2. Step 2: Convert to fraction form
   309,708/678,432 = 678,432/x
3. Step 3: Cross multiply
   309,708x = 678,432 × 678,432
4. Step 4: Simplify right side
   309,708x = 460,269,978,624
5. Step 5: Solve for x
   x = 460,269,978,624/309,708
6. Step 6: Final answer
   x = 1,486,141.72