Finding the Fourth Proportional to 1,139.73, 1,572.71 and 642.39

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.73 : 1,572.71 = 642.39 : x
2. Step 2: Convert to fraction form
   1,139.73/1,572.71 = 642.39/x
3. Step 3: Cross multiply
   1,139.73x = 1,572.71 × 642.39
4. Step 4: Simplify right side
   1,139.73x = 1,010,293.18
5. Step 5: Solve for x
   x = 1,010,293.18/1,139.73
6. Step 6: Final answer
   x = 886.43