Finding the Fourth Proportional to 1,390.13, 1,918.59 and 800.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.13 : 1,918.59 = 800.55 : x
2. Step 2: Convert to fraction form
   1,390.13/1,918.59 = 800.55/x
3. Step 3: Cross multiply
   1,390.13x = 1,918.59 × 800.55
4. Step 4: Simplify right side
   1,390.13x = 1,535,924.22
5. Step 5: Solve for x
   x = 1,535,924.22/1,390.13
6. Step 6: Final answer
   x = 1,104.88