Finding the Fourth Proportional to 1,428.93, 1,971.78 and 831.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.93 : 1,971.78 = 831.30 : x
2. Step 2: Convert to fraction form
   1,428.93/1,971.78 = 831.30/x
3. Step 3: Cross multiply
   1,428.93x = 1,971.78 × 831.30
4. Step 4: Simplify right side
   1,428.93x = 1,639,140.71
5. Step 5: Solve for x
   x = 1,639,140.71/1,428.93
6. Step 6: Final answer
   x = 1,147.11