Finding the Fourth Proportional to 1,390.89, 1,919.14 and 831.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.89 : 1,919.14 = 831.15 : x
2. Step 2: Convert to fraction form
   1,390.89/1,919.14 = 831.15/x
3. Step 3: Cross multiply
   1,390.89x = 1,919.14 × 831.15
4. Step 4: Simplify right side
   1,390.89x = 1,595,093.21
5. Step 5: Solve for x
   x = 1,595,093.21/1,390.89
6. Step 6: Final answer
   x = 1,146.81