Finding the Fourth Proportional to 1,380.66, 1,905.31 and 791.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.66 : 1,905.31 = 791.20 : x
2. Step 2: Convert to fraction form
   1,380.66/1,905.31 = 791.20/x
3. Step 3: Cross multiply
   1,380.66x = 1,905.31 × 791.20
4. Step 4: Simplify right side
   1,380.66x = 1,507,481.27
5. Step 5: Solve for x
   x = 1,507,481.27/1,380.66
6. Step 6: Final answer
   x = 1,091.86