Finding the Fourth Proportional to 1,388.81, 1,916.60 and 865.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.81 : 1,916.60 = 865.15 : x
2. Step 2: Convert to fraction form
   1,388.81/1,916.60 = 865.15/x
3. Step 3: Cross multiply
   1,388.81x = 1,916.60 × 865.15
4. Step 4: Simplify right side
   1,388.81x = 1,658,137.37
5. Step 5: Solve for x
   x = 1,658,137.37/1,388.81
6. Step 6: Final answer
   x = 1,193.92