Finding the Fourth Proportional to 1,139.77, 1,572.82 and 642.43

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.77 : 1,572.82 = 642.43 : x
2. Step 2: Convert to fraction form
   1,139.77/1,572.82 = 642.43/x
3. Step 3: Cross multiply
   1,139.77x = 1,572.82 × 642.43
4. Step 4: Simplify right side
   1,139.77x = 1,010,426.75
5. Step 5: Solve for x
   x = 1,010,426.75/1,139.77
6. Step 6: Final answer
   x = 886.52