Finding the Fourth Proportional to 1,389.62, 1,916.78 and 1,057.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.62 : 1,916.78 = 1,057.31 : x
2. Step 2: Convert to fraction form
   1,389.62/1,916.78 = 1,057.31/x
3. Step 3: Cross multiply
   1,389.62x = 1,916.78 × 1,057.31
4. Step 4: Simplify right side
   1,389.62x = 2,026,630.66
5. Step 5: Solve for x
   x = 2,026,630.66/1,389.62
6. Step 6: Final answer
   x = 1,458.41