Finding the Fourth Proportional to 2,087.28, 2,879.28 and 1,389.12

Step by Step Solution

1. Step 1: Write the proportion equation
   2,087.28 : 2,879.28 = 1,389.12 : x
2. Step 2: Convert to fraction form
   2,087.28/2,879.28 = 1,389.12/x
3. Step 3: Cross multiply
   2,087.28x = 2,879.28 × 1,389.12
4. Step 4: Simplify right side
   2,087.28x = 3,999,665.43
5. Step 5: Solve for x
   x = 3,999,665.43/2,087.28
6. Step 6: Final answer
   x = 1,916.21