Finding the Fourth Proportional to 1,020.79, 1,408.76 and 578.76

Step by Step Solution

1. Step 1: Write the proportion equation
   1,020.79 : 1,408.76 = 578.76 : x
2. Step 2: Convert to fraction form
   1,020.79/1,408.76 = 578.76/x
3. Step 3: Cross multiply
   1,020.79x = 1,408.76 × 578.76
4. Step 4: Simplify right side
   1,020.79x = 815,333.94
5. Step 5: Solve for x
   x = 815,333.94/1,020.79
6. Step 6: Final answer
   x = 798.73