Finding the Fourth Proportional to 1,399.28, 1,931.13 and 809.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,399.28 : 1,931.13 = 809.78 : x
2. Step 2: Convert to fraction form
   1,399.28/1,931.13 = 809.78/x
3. Step 3: Cross multiply
   1,399.28x = 1,931.13 × 809.78
4. Step 4: Simplify right side
   1,399.28x = 1,563,780.80
5. Step 5: Solve for x
   x = 1,563,780.80/1,399.28
6. Step 6: Final answer
   x = 1,117.57