Finding the Fourth Proportional to 1,020.78, 1,408.04 and 890.10

Step by Step Solution

1. Step 1: Write the proportion equation
   1,020.78 : 1,408.04 = 890.10 : x
2. Step 2: Convert to fraction form
   1,020.78/1,408.04 = 890.10/x
3. Step 3: Cross multiply
   1,020.78x = 1,408.04 × 890.10
4. Step 4: Simplify right side
   1,020.78x = 1,253,296.40
5. Step 5: Solve for x
   x = 1,253,296.40/1,020.78
6. Step 6: Final answer
   x = 1,227.78