Finding the Fourth Proportional to 1,385.23, 1,909.60 and 991.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,385.23 : 1,909.60 = 991.57 : x
2. Step 2: Convert to fraction form
   1,385.23/1,909.60 = 991.57/x
3. Step 3: Cross multiply
   1,385.23x = 1,909.60 × 991.57
4. Step 4: Simplify right side
   1,385.23x = 1,893,502.07
5. Step 5: Solve for x
   x = 1,893,502.07/1,385.23
6. Step 6: Final answer
   x = 1,366.92