Finding the Fourth Proportional to 1,387.20, 1,915.56 and 864.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.20 : 1,915.56 = 864.12 : x
2. Step 2: Convert to fraction form
   1,387.20/1,915.56 = 864.12/x
3. Step 3: Cross multiply
   1,387.20x = 1,915.56 × 864.12
4. Step 4: Simplify right side
   1,387.20x = 1,655,273.71
5. Step 5: Solve for x
   x = 1,655,273.71/1,387.20
6. Step 6: Final answer
   x = 1,193.25