Finding the Fourth Proportional to 1,131.20, 1,696.56 and 390.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,131.20 : 1,696.56 = 390.72 : x
2. Step 2: Convert to fraction form
   1,131.20/1,696.56 = 390.72/x
3. Step 3: Cross multiply
   1,131.20x = 1,696.56 × 390.72
4. Step 4: Simplify right side
   1,131.20x = 662,879.92
5. Step 5: Solve for x
   x = 662,879.92/1,131.20
6. Step 6: Final answer
   x = 586.00