Finding the Third Proportional to 258,288 and 399,144

Step by Step Solution

1. Step 1: Write the proportion equation
   258,288 : 399,144 = 399,144 : x
2. Step 2: Convert to fraction form
   258,288/399,144 = 399,144/x
3. Step 3: Cross multiply
   258,288x = 399,144 × 399,144
4. Step 4: Simplify right side
   258,288x = 159,315,932,736
5. Step 5: Solve for x
   x = 159,315,932,736/258,288
6. Step 6: Final answer
   x = 616,815.08