Finding the Fourth Proportional to 1,387.87, 1,915.47 and 864.07

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.87 : 1,915.47 = 864.07 : x
2. Step 2: Convert to fraction form
   1,387.87/1,915.47 = 864.07/x
3. Step 3: Cross multiply
   1,387.87x = 1,915.47 × 864.07
4. Step 4: Simplify right side
   1,387.87x = 1,655,100.16
5. Step 5: Solve for x
   x = 1,655,100.16/1,387.87
6. Step 6: Final answer
   x = 1,192.55