Finding the Fourth Proportional to 1,390.20, 1,917.88 and 800.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.20 : 1,917.88 = 800.61 : x
2. Step 2: Convert to fraction form
   1,390.20/1,917.88 = 800.61/x
3. Step 3: Cross multiply
   1,390.20x = 1,917.88 × 800.61
4. Step 4: Simplify right side
   1,390.20x = 1,535,473.91
5. Step 5: Solve for x
   x = 1,535,473.91/1,390.20
6. Step 6: Final answer
   x = 1,104.50