Finding the Fourth Proportional to 1,290.79, 1,780.81 and 825.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.79 : 1,780.81 = 825.31 : x
2. Step 2: Convert to fraction form
   1,290.79/1,780.81 = 825.31/x
3. Step 3: Cross multiply
   1,290.79x = 1,780.81 × 825.31
4. Step 4: Simplify right side
   1,290.79x = 1,469,720.30
5. Step 5: Solve for x
   x = 1,469,720.30/1,290.79
6. Step 6: Final answer
   x = 1,138.62