Finding the Fourth Proportional to 1,391.89, 1,918.81 and 860.42

Step by Step Solution

1. Step 1: Write the proportion equation
   1,391.89 : 1,918.81 = 860.42 : x
2. Step 2: Convert to fraction form
   1,391.89/1,918.81 = 860.42/x
3. Step 3: Cross multiply
   1,391.89x = 1,918.81 × 860.42
4. Step 4: Simplify right side
   1,391.89x = 1,650,972.91
5. Step 5: Solve for x
   x = 1,650,972.91/1,391.89
6. Step 6: Final answer
   x = 1,186.14