Finding the Fourth Proportional to 1,020.78, 1,408.59 and 578.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,020.78 : 1,408.59 = 578.61 : x
2. Step 2: Convert to fraction form
   1,020.78/1,408.59 = 578.61/x
3. Step 3: Cross multiply
   1,020.78x = 1,408.59 × 578.61
4. Step 4: Simplify right side
   1,020.78x = 815,024.26
5. Step 5: Solve for x
   x = 815,024.26/1,020.78
6. Step 6: Final answer
   x = 798.43