Finding the Fourth Proportional to 1,385.39, 1,909.20 and 991.73

Step by Step Solution

1. Step 1: Write the proportion equation
   1,385.39 : 1,909.20 = 991.73 : x
2. Step 2: Convert to fraction form
   1,385.39/1,909.20 = 991.73/x
3. Step 3: Cross multiply
   1,385.39x = 1,909.20 × 991.73
4. Step 4: Simplify right side
   1,385.39x = 1,893,410.92
5. Step 5: Solve for x
   x = 1,893,410.92/1,385.39
6. Step 6: Final answer
   x = 1,366.70