Finding the Fourth Proportional to 1,139.87, 1,572.88 and 642.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.87 : 1,572.88 = 642.55 : x
2. Step 2: Convert to fraction form
   1,139.87/1,572.88 = 642.55/x
3. Step 3: Cross multiply
   1,139.87x = 1,572.88 × 642.55
4. Step 4: Simplify right side
   1,139.87x = 1,010,650.83
5. Step 5: Solve for x
   x = 1,010,650.83/1,139.87
6. Step 6: Final answer
   x = 886.64