Finding the Fourth Proportional to 1,380.79, 1,905.47 and 791.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.79 : 1,905.47 = 791.31 : x
2. Step 2: Convert to fraction form
   1,380.79/1,905.47 = 791.31/x
3. Step 3: Cross multiply
   1,380.79x = 1,905.47 × 791.31
4. Step 4: Simplify right side
   1,380.79x = 1,507,807.94
5. Step 5: Solve for x
   x = 1,507,807.94/1,380.79
6. Step 6: Final answer
   x = 1,091.99