Finding the Fourth Proportional to 1,391.55, 1,920.04 and 853.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,391.55 : 1,920.04 = 853.31 : x
2. Step 2: Convert to fraction form
   1,391.55/1,920.04 = 853.31/x
3. Step 3: Cross multiply
   1,391.55x = 1,920.04 × 853.31
4. Step 4: Simplify right side
   1,391.55x = 1,638,381.42
5. Step 5: Solve for x
   x = 1,638,381.42/1,391.55
6. Step 6: Final answer
   x = 1,177.37