Finding the Fourth Proportional to 1,389.78, 1,921.50 and 1,328.58

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.78 : 1,921.50 = 1,328.58 : x
2. Step 2: Convert to fraction form
   1,389.78/1,921.50 = 1,328.58/x
3. Step 3: Cross multiply
   1,389.78x = 1,921.50 × 1,328.58
4. Step 4: Simplify right side
   1,389.78x = 2,552,866.47
5. Step 5: Solve for x
   x = 2,552,866.47/1,389.78
6. Step 6: Final answer
   x = 1,836.89