Finding the Fourth Proportional to 1,380.78, 1,905.39 and 791.28

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.78 : 1,905.39 = 791.28 : x
2. Step 2: Convert to fraction form
   1,380.78/1,905.39 = 791.28/x
3. Step 3: Cross multiply
   1,380.78x = 1,905.39 × 791.28
4. Step 4: Simplify right side
   1,380.78x = 1,507,697.00
5. Step 5: Solve for x
   x = 1,507,697.00/1,380.78
6. Step 6: Final answer
   x = 1,091.92