Finding the Fourth Proportional to 1,389.31, 1,917.60 and 858.65

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.31 : 1,917.60 = 858.65 : x
2. Step 2: Convert to fraction form
   1,389.31/1,917.60 = 858.65/x
3. Step 3: Cross multiply
   1,389.31x = 1,917.60 × 858.65
4. Step 4: Simplify right side
   1,389.31x = 1,646,534.43
5. Step 5: Solve for x
   x = 1,646,534.43/1,389.31
6. Step 6: Final answer
   x = 1,185.15