Finding the Fourth Proportional to 1,390.25, 1,918.71 and 800.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.25 : 1,918.71 = 800.78 : x
2. Step 2: Convert to fraction form
   1,390.25/1,918.71 = 800.78/x
3. Step 3: Cross multiply
   1,390.25x = 1,918.71 × 800.78
4. Step 4: Simplify right side
   1,390.25x = 1,536,455.00
5. Step 5: Solve for x
   x = 1,536,455.00/1,390.25
6. Step 6: Final answer
   x = 1,105.17