Finding the Fourth Proportional to 1,120.34, 1,680.69 and 390.35

Step by Step Solution

1. Step 1: Write the proportion equation
   1,120.34 : 1,680.69 = 390.35 : x
2. Step 2: Convert to fraction form
   1,120.34/1,680.69 = 390.35/x
3. Step 3: Cross multiply
   1,120.34x = 1,680.69 × 390.35
4. Step 4: Simplify right side
   1,120.34x = 656,057.34
5. Step 5: Solve for x
   x = 656,057.34/1,120.34
6. Step 6: Final answer
   x = 585.59