Finding the Fourth Proportional to 1,387.80, 1,915.42 and 798.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.80 : 1,915.42 = 798.72 : x
2. Step 2: Convert to fraction form
   1,387.80/1,915.42 = 798.72/x
3. Step 3: Cross multiply
   1,387.80x = 1,915.42 × 798.72
4. Step 4: Simplify right side
   1,387.80x = 1,529,884.26
5. Step 5: Solve for x
   x = 1,529,884.26/1,387.80
6. Step 6: Final answer
   x = 1,102.38