Finding the Fourth Proportional to 1,389.30, 1,917.35 and 791.90

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.30 : 1,917.35 = 791.90 : x
2. Step 2: Convert to fraction form
   1,389.30/1,917.35 = 791.90/x
3. Step 3: Cross multiply
   1,389.30x = 1,917.35 × 791.90
4. Step 4: Simplify right side
   1,389.30x = 1,518,335.92
5. Step 5: Solve for x
   x = 1,518,335.92/1,389.30
6. Step 6: Final answer
   x = 1,092.88