Finding the Fourth Proportional to 1,139.68, 1,572.71 and 642.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.68 : 1,572.71 = 642.31 : x
2. Step 2: Convert to fraction form
   1,139.68/1,572.71 = 642.31/x
3. Step 3: Cross multiply
   1,139.68x = 1,572.71 × 642.31
4. Step 4: Simplify right side
   1,139.68x = 1,010,160.22
5. Step 5: Solve for x
   x = 1,010,160.22/1,139.68
6. Step 6: Final answer
   x = 886.36