Finding the Third Proportional to 401,978 and 639,868

Step by Step Solution

1. Step 1: Write the proportion equation
   401,978 : 639,868 = 639,868 : x
2. Step 2: Convert to fraction form
   401,978/639,868 = 639,868/x
3. Step 3: Cross multiply
   401,978x = 639,868 × 639,868
4. Step 4: Simplify right side
   401,978x = 409,431,057,424
5. Step 5: Solve for x
   x = 409,431,057,424/401,978
6. Step 6: Final answer
   x = 1,018,540.96