Finding the Fourth Proportional to 1,389.20, 2,073.78 and 1,287.86

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.20 : 2,073.78 = 1,287.86 : x
2. Step 2: Convert to fraction form
   1,389.20/2,073.78 = 1,287.86/x
3. Step 3: Cross multiply
   1,389.20x = 2,073.78 × 1,287.86
4. Step 4: Simplify right side
   1,389.20x = 2,670,738.31
5. Step 5: Solve for x
   x = 2,670,738.31/1,389.20
6. Step 6: Final answer
   x = 1,922.50