Finding the Fourth Proportional to 1,428.18, 2,139.54 and 812.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.18 : 2,139.54 = 812.31 : x
2. Step 2: Convert to fraction form
   1,428.18/2,139.54 = 812.31/x
3. Step 3: Cross multiply
   1,428.18x = 2,139.54 × 812.31
4. Step 4: Simplify right side
   1,428.18x = 1,737,969.74
5. Step 5: Solve for x
   x = 1,737,969.74/1,428.18
6. Step 6: Final answer
   x = 1,216.91