Finding the Fourth Proportional to 1,387.76, 2,078.89 and 728.65

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.76 : 2,078.89 = 728.65 : x
2. Step 2: Convert to fraction form
   1,387.76/2,078.89 = 728.65/x
3. Step 3: Cross multiply
   1,387.76x = 2,078.89 × 728.65
4. Step 4: Simplify right side
   1,387.76x = 1,514,774.33
5. Step 5: Solve for x
   x = 1,514,774.33/1,387.76
6. Step 6: Final answer
   x = 1,091.53