Finding the Fourth Proportional to 1,123.61, 1,686.18 and 393.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,123.61 : 1,686.18 = 393.20 : x
2. Step 2: Convert to fraction form
   1,123.61/1,686.18 = 393.20/x
3. Step 3: Cross multiply
   1,123.61x = 1,686.18 × 393.20
4. Step 4: Simplify right side
   1,123.61x = 662,999.65
5. Step 5: Solve for x
   x = 662,999.65/1,123.61
6. Step 6: Final answer
   x = 590.06