Finding the Fourth Proportional to 1,390.87, 1,919.35 and 831.21

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.87 : 1,919.35 = 831.21 : x
2. Step 2: Convert to fraction form
   1,390.87/1,919.35 = 831.21/x
3. Step 3: Cross multiply
   1,390.87x = 1,919.35 × 831.21
4. Step 4: Simplify right side
   1,390.87x = 1,595,389.89
5. Step 5: Solve for x
   x = 1,595,389.89/1,390.87
6. Step 6: Final answer
   x = 1,147.04