Finding the Fourth Proportional to 1,120.38, 1,680.50 and 390.03

Step by Step Solution

1. Step 1: Write the proportion equation
   1,120.38 : 1,680.50 = 390.03 : x
2. Step 2: Convert to fraction form
   1,120.38/1,680.50 = 390.03/x
3. Step 3: Cross multiply
   1,120.38x = 1,680.50 × 390.03
4. Step 4: Simplify right side
   1,120.38x = 655,443.46
5. Step 5: Solve for x
   x = 655,443.46/1,120.38
6. Step 6: Final answer
   x = 585.02