Finding the Fourth Proportional to 1,391.10, 1,918.79 and 831.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,391.10 : 1,918.79 = 831.12 : x
2. Step 2: Convert to fraction form
   1,391.10/1,918.79 = 831.12/x
3. Step 3: Cross multiply
   1,391.10x = 1,918.79 × 831.12
4. Step 4: Simplify right side
   1,391.10x = 1,594,744.74
5. Step 5: Solve for x
   x = 1,594,744.74/1,391.10
6. Step 6: Final answer
   x = 1,146.39