Finding the Fourth Proportional to 1,120.57, 1,680.33 and 390.05

Step by Step Solution

1. Step 1: Write the proportion equation
   1,120.57 : 1,680.33 = 390.05 : x
2. Step 2: Convert to fraction form
   1,120.57/1,680.33 = 390.05/x
3. Step 3: Cross multiply
   1,120.57x = 1,680.33 × 390.05
4. Step 4: Simplify right side
   1,120.57x = 655,412.72
5. Step 5: Solve for x
   x = 655,412.72/1,120.57
6. Step 6: Final answer
   x = 584.89